Parameterize data-based tests and make data path configurable

[krystophny]

Summary

Closes #6

This change makes the data-based test suite configurable and properly
parameterized:

• Configurable data/code paths via command line. The data_path and
  code_path fixtures in tests/conftest.py now accept the new
  --data-path / --code-path pytest command-line options (as suggested
  by the linked StackOverflow discussion) and fall back to the DATA /
  CODE environment variables when the options are not given. This makes
  it possible to point the tests at the "standard data" directory on any
  machine without relying on fixed environment variables.

• Parameterized tests over standard data. The EQDSK tests
  (test_eqdsk_read, test_eqdsk_golden_records) and the
  efit_to_boozer q-profile comparison are now driven by
  @pytest.mark.parametrize over the set of standard reference data
  files instead of looping manually. Each data file is reported as its
  own test case, so failures are easier to isolate and individual files
  can be selected or deselected.

• Move tests upstream / clean standalone tests. The standalone NEO-RT
  benchmark test_util no longer invokes the test at module import time,
  so it runs exactly once as a proper pytest test and does not execute
  when merely imported elsewhere.

Tests

• Verified --data-path / --code-path options work and produce a clear
  UsageError when neither an option nor the environment variable is set.
• Verified the parametrize pattern collects each standard data file as a
  separate test case.
• Ran the standalone NEO-RT benchmark test_util.py with pytest
  (1 passed).
• The libneo-based tests could not be executed here because the
  libneo Python module is not shipped in this repository (it is cloned
  separately in CI), but the changes are syntactically valid and follow
  the existing parametrize pattern.

[krystophny]

Review verdict: Comment

Summary: The test-only changes are scoped and syntactically sound; parameterization and path overrides preserve existing behavior.

Findings: No findings.

Verdict: Comment — no defect found, but CI is still in progress and libneo tests could not be run locally.