feat: use real Cartesian Boozer chartmaps

[krystophny]

Summary

Switch the Boozer chartmap export/import path to the real Cartesian embedding of the Boozer grid and tighten the end-to-end benchmark artifacts on top of the stacked SIMPLE work.

This top layer does two things:

• replace the earlier pseudo-Cartesian Boozer export with the true physical Cartesian map
• finalize the benchmark/golden artifacts around the cases that are actually trustworthy

Dependencies

SIMPLE stack

• depends on SIMPLE PR 331

libneo dependency

The required libneo support is already merged on main.

That libneo change accepts zeta_convention='boozer', keeps the fast cyl and vmec paths unchanged, and routes the generalized Boozer case through the real Cartesian chartmap inversion path.

What changed in this top layer

• export VMEC Boozer chartmaps with real Cartesian x,y,z
• keep the GVEC converter on the same real-Cartesian contract
• tighten the VMEC roundtrip field tolerance back to 1e-4 for QA, QH, and NCSX
• keep the shared VMEC/GVEC benchmark on QA, where the downstream SIMPLE comparison is exact
• keep QH and NCSX as strict VMEC-direct vs VMEC-chartmap end-to-end coverage
• refresh the figure-8 golden chartmap and review plots for the real-Cartesian path
• generate reviewer-facing artifacts under the CTest build tree, including multi-view 3D geometry sheets and combined loss plots

Final benchmark scope

Shared QA case

Compared across all three paths:

1. direct VMEC Boozer
2. VMEC-exported Boozer chartmap
3. GVEC-exported Boozer chartmap

Observed on the current branch:

• VMEC direct vs VMEC chartmap: max relative |B| = 7.20e-5, max |Δs| = 1.67e-9
• VMEC direct vs GVEC chartmap: max relative |B| = 1.47e-4, max |Δs| = 5.50e-10
• confined/lost fractions: exact match across all three runs

VMEC-only coverage

These remain strict direct-vs-file end-to-end checks:

• QH: max relative |B| = 9.51e-5, max |Δs| = 6.97e-9
• NCSX: max relative |B| = 9.79e-5, max |Δs| = 3.72e-7

Figure-8 GVEC golden case

• QUASR boundary -> GVEC solve -> Boozer chartmap -> simple.x
• golden signature refreshed to the real-Cartesian export
• review artifact now shows the figure-8 geometry explicitly in x-z, y-z, and multiple 3D views

Verification

ctest --test-dir build --output-on-failure -R '^(test_e2e_boozer_chartmap|test_figure8_boozer_chartmap)$'

Result:

• 100% tests passed, 0 tests failed out of 2

make test-fast

Result:

• 100% tests passed, 0 tests failed out of 38

Review

Primary GVEC/QUASR review: @Rykath
SIMPLE-maintainer follow-up: @krystophny