Refactor codebase to improve performance, maintainability and usability

[flferretti]

This PR enhances the codebase by fixing typos, refactoring classes, and optimizing Gazebo SDF processing with caching and batch support. Moreover, it updates the build system to use hatchling and improves the command-line interface.

First loading run:

# %timeit -n1 -r1 rod.Sdf.load(model_path)
< 678 ms ± 0 ns per loop (mean ± std. dev. of 1 run, 1 loop each)
> 592 ms ± 0 ns per loop (mean ± std. dev. of 1 run, 1 loop each)

Successive loading run:

# %timeit rod.Sdf.load(model_path)
< 657 ms ± 39.7 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
> 12.1 ms ± 396 μs per loop (mean ± std. dev. of 7 runs, 100 loops each)

Switching model frame convention to URDF:

# %timeit sdf.model.switch_frame_convention(frame_convention=rod.FrameConvention.Urdf)
< 196 ms ± 4.98 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)
> 168 ms ± 9.18 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

Exporting to URDF:

# %timeit UrdfExporter(pretty=True, gazebo_preserve_fixed_joints=True).to_urdf_string(sdf=sdf)
< 237 ms ± 2.44 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
> 206 ms ± 9.41 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

Test Script

import icub_models
import rod
from rod.urdf.exporter import UrdfExporter

model_path = icub_models.get_model_file("iCubGazeboV2_5")

# First loading run
%timeit -n1 -r1 _ = rod.Sdf.load(model_path)

# Successive loading run
%timeit _ = rod.Sdf.load(model_path)

sdf = rod.Sdf.load(model_path)

# Switching model frame convention to URDF
%timeit sdf.model.switch_frame_convention(frame_convention=rod.FrameConvention.Urdf)

# Exporting to URDF
%timeit _ = UrdfExporter(pretty=True, gazebo_preserve_fixed_joints=True).to_urdf_string(sdf=sdf)