feat(io): add limited native IBW v5 image parser

[kegouro]

Summary

Adds a limited native Igor Binary Wave v5 image parser.

The implementation is frozen at:

7c2b38597ad2aa168d8b944cecfb1e9054149fb7

Implemented scope

• IBW v5
• little-endian
• FP32
• demonstrated 2D image layout
• native header-gated reader
• standard library + NumPy only
• unsupported variants retain the optional afmformats fallback

Development evidence

Using only the four preregistered DEVELOPMENT files:

• 4/4 files parsed
• 15/15 channel matrices matched Gwyddion 2.71 exactly
• pixel maximum delta: 0.0 nm
• pixel RMS delta: 0.0 nm
• Sa/Sq/Sz: 36/36 within the frozen tolerance
• focused tests: 13 passed
• no-GUI suite: 292 passed, 26 skipped
• package gate: passed

This evidence grants only SOFTWARE_VERIFIED status before blind execution.

Blinding state

• BLIND_HOLDOUT opened: 0/2
• BLIND_RESERVE opened: 0/8
• parser changes after frozen implementation commit: none

Frozen Validation protocol:

kegouro/spmkit-validation#2

Claim boundary

This PR does not yet establish:

• Level 2 or Level 3 parser evidence
• general IBW compatibility
• big-endian or non-FP32 support
• force-spectroscopy support
• physical validation

No raw candidate data is included.

Keep this PR as Draft and do not merge until the blind holdout is executed,
recorded and audited.

[kegouro]

Preregistered Validation freeze: kegouro/spmkit-validation#2

Freeze: c1fea8f17be38712888bf128919158ad5dbdb6b0
Corrigendum: e9706e82028dedd2fc4dada13d4c9d6bb86fdcd6

Do not merge before blind-holdout execution and audit.