refactor: improve spherical interpolation

[henry2004y]

• Remove _ensure_full_phi by using built-in periodic extrapolation support from Interpolations.jl
• Support high-order spherical interpolations

[gemini-code-assist]

Summary of Changes

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This pull request refactors the spherical interpolation logic by removing a custom function that handled periodic boundary conditions for the phi coordinate. Instead, it now utilizes the native periodic extrapolation features provided by the Interpolations.jl library, leading to cleaner and potentially more robust code. Additionally, minor formatting and performance improvements were applied to other interpolation-related functions.

Highlights

• Spherical Interpolation Refinement: The custom _ensure_full_phi function has been removed, leveraging the built-in periodic extrapolation support from the Interpolations.jl package for handling the phi dimension in spherical coordinates.
• Code Simplification: The build_interpolator function for spherical grids now directly uses Periodic(OnGrid()) or Periodic(OnCell()) boundary conditions, simplifying the logic for handling periodic phi ranges.
• Performance Improvement: The @inbounds macro was added to the FieldInterpolator1D call operator for potential performance gains by skipping bounds checks.

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Changelog

• src/utility/interpolation.jl
  • Removed the _ensure_full_phi function, which previously handled periodic extrapolation for the phi dimension.
  • Modified the build_interpolator function for spherical grids to use Periodic(OnGrid()) or Periodic(OnCell()) boundary conditions for the phi coordinate, depending on the grid's extent.
  • Added the @inbounds macro to the FieldInterpolator1D call operator for improved performance.
  • Relocated the build_interpolator definition for CartesianGrid to a more appropriate position after SphericalFieldInterpolator.
  • Adjusted the formatting of several build_interpolator function signatures for better readability.

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[gemini-code-assist]

Code Review

This pull request refactors the spherical interpolation logic to use the built-in periodic extrapolation support from Interpolations.jl, which is a great improvement that simplifies the code by removing the manual _ensure_full_phi function. However, this change has also unintentionally removed support for higher-order interpolation on uniform spherical grids, as the new implementation always uses linear interpolation. My review includes a suggestion to restore this functionality while retaining the benefits of the refactoring for non-uniform grids. Other changes are minor improvements like code formatting and adding @inbounds for performance.

[github-actions]

Benchmark Results (Julia v1)

Time benchmarks

	master	b3752b8...	master / b3752b8...
interpolation/cartesian	0.13 ± 0.011 μs	0.12 ± 0.001 μs	1.08 ± 0.092
interpolation/spherical	0.411 ± 0.001 μs	0.411 ± 0.001 μs	1 ± 0.0034
interpolation/time-dependent	4.1 ± 3.9 μs	4.41 ± 3.7 μs	0.93 ± 1.2
trace/GC/DiffEq Vern6	5.62 ± 1.8 μs	5.58 ± 1.9 μs	1.01 ± 0.46
trace/GC/Native RK4	0.137 ± 0.00016 s	0.137 ± 0.00017 s	0.999 ± 0.0017
trace/GC/Native RK45	3.52 ± 0.13 μs	3.37 ± 0.14 μs	1.04 ± 0.058
trace/Hybrid/Sheared	2.24 ± 0.08 μs	2.02 ± 0.09 μs	1.11 ± 0.063
trace/analytic field/in place	0.0597 ± 0.04 ms	0.0564 ± 0.04 ms	1.06 ± 1
trace/analytic field/in place relativistic	0.0792 ± 0.031 ms	0.0794 ± 0.036 ms	0.997 ± 0.6
trace/analytic field/out of place	0.0585 ± 0.038 ms	0.0484 ± 0.04 ms	1.21 ± 1.3
trace/normalized/out of place	18.5 ± 11 μs	15.9 ± 9.9 μs	1.16 ± 0.98
trace/numerical field/Adaptive Boris	4.2 ± 0.13 ms	4.19 ± 0.1 ms	1 ± 0.04
trace/numerical field/Boris	7.39 ± 0.07 μs	7.36 ± 0.07 μs	1 ± 0.013
trace/numerical field/Boris ensemble	14.7 ± 0.11 μs	14.7 ± 0.13 μs	1 ± 0.012
trace/numerical field/Boris kernel	9.64 ± 0.13 μs	9.56 ± 0.12 μs	1.01 ± 0.019
trace/numerical field/Boris with fields	8.02 ± 0.08 μs	8.04 ± 0.08 μs	0.996 ± 0.014
trace/numerical field/Multistep Boris	11 ± 0.081 μs	10.9 ± 0.09 μs	1 ± 0.011
trace/numerical field/in place	25.3 ± 5.7 μs	25 ± 5.7 μs	1.01 ± 0.32
trace/numerical field/out of place	18.5 ± 5.5 μs	18.1 ± 5.6 μs	1.02 ± 0.44
trace/time-dependent field/in place	0.136 ± 0.0034 ms	0.133 ± 0.004 ms	1.02 ± 0.04
trace/time-dependent field/out of place	0.123 ± 0.0061 ms	0.108 ± 0.0033 ms	1.14 ± 0.067
time_to_load	1.86 ± 0.0073 s	1.86 ± 0.0032 s	0.996 ± 0.0043

Memory benchmarks

	master	b3752b8...	master / b3752b8...
interpolation/cartesian	2 allocs: 0.234 kB	2 allocs: 0.234 kB	1
interpolation/spherical	2 allocs: 0.203 kB	2 allocs: 0.203 kB	1
interpolation/time-dependent	0.044 k allocs: 9.62 kB	0.044 k allocs: 9.62 kB	1
trace/GC/DiffEq Vern6	0.174 k allocs: 12.2 kB	0.174 k allocs: 12.2 kB	1
trace/GC/Native RK4	13 allocs: 0.382 MB	13 allocs: 0.382 MB	1
trace/GC/Native RK45	16 allocs: 2.44 kB	16 allocs: 2.44 kB	1
trace/Hybrid/Sheared	8 allocs: 2.98 kB	8 allocs: 2.98 kB	1
trace/analytic field/in place	2.07 k allocs: 0.091 MB	2.07 k allocs: 0.091 MB	1
trace/analytic field/in place relativistic	2.07 k allocs: 0.091 MB	2.07 k allocs: 0.091 MB	1
trace/analytic field/out of place	2.04 k allocs: 0.0894 MB	2.04 k allocs: 0.0894 MB	1
trace/normalized/out of place	0.756 k allocs: 0.0332 MB	0.756 k allocs: 0.0332 MB	1
trace/numerical field/Adaptive Boris	27 allocs: 1.5 MB	27 allocs: 1.5 MB	1
trace/numerical field/Boris	6 allocs: 1.16 kB	6 allocs: 1.16 kB	1
trace/numerical field/Boris ensemble	10 allocs: 2.28 kB	10 allocs: 2.28 kB	1
trace/numerical field/Boris kernel	0.038 k allocs: 2.12 kB	0.038 k allocs: 2.12 kB	1
trace/numerical field/Boris with fields	6 allocs: 1.52 kB	6 allocs: 1.52 kB	1
trace/numerical field/Multistep Boris	6 allocs: 1.16 kB	6 allocs: 1.16 kB	1
trace/numerical field/in place	0.411 k allocs: 20.4 kB	0.411 k allocs: 20.4 kB	1
trace/numerical field/out of place	0.378 k allocs: 18.4 kB	0.378 k allocs: 18.4 kB	1
trace/time-dependent field/in place	3.95 k allocs: 0.181 MB	3.95 k allocs: 0.181 MB	1
trace/time-dependent field/out of place	3.92 k allocs: 0.179 MB	3.92 k allocs: 0.179 MB	1
time_to_load	0.149 k allocs: 11.1 kB	0.145 k allocs: 11 kB	1.02

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.30%. Comparing base (c3283cd) to head (b3752b8).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #485      +/-   ##
==========================================
+ Coverage   83.50%   84.30%   +0.79%     
==========================================
  Files          18       18              
  Lines        1898     1880      -18     
==========================================
  Hits         1585     1585              
+ Misses        313      295      -18     

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