Correctly parse fchk files without whitespace between values

[tovrstra]

The test file was generated with Psi4 and has been stripped down below 100k with a new tool tools/stripfchk.py included in this PR.

[Copilot]

🟡 Changes recommended

The new float tokenizer accepts D/d exponents via the regex but still passes tokens directly to float(), which will fail on Fortran-style D exponents.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR improves IOData’s FCHK reader robustness for real-valued array fields by correctly tokenizing floating-point numbers even when adjacent values are not separated by whitespace (as can happen with large exponents), and adds a minimized Psi4-generated FCHK fixture plus a helper script to keep test data under the repository size limit.

Changes:

• Update iodata/formats/fchk.py to extract float array values via a regex tokenizer instead of whitespace splitting.
• Add a Psi4-derived FCHK test fixture and a new regression test that validates correct parsing (including orthonormal MO checks).
• Introduce tools/stripfchk.py to strip irrelevant FCHK fields while preserving formatting quirks needed for parser regression tests.

File summaries

File	Description
tools/stripfchk.py	New utility to strip/retain selected FCHK fields to keep test fixtures small while preserving raw formatting.
iodata/test/test_fchk.py	New regression test covering Psi4 FCHK parsing when float values are adjacent without whitespace.
iodata/test/data/psi4_hcch.fchk	New stripped Psi4-generated fixture exhibiting adjacent-float formatting edge cases.
iodata/formats/fchk.py	Switch float-array tokenization to a regex-based approach to handle missing whitespace between values.

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 1
• Review effort level: Lite

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[tovrstra]

Failing tests will pass after #407 has been merged.

[PaulWAyers]

LGTM.

[tovrstra]

Thanks for checking. I just reran the tests against the main branch after merging #407. All pass.