test: slim testIDT.cpp — spot-checks and fingerprints (#276)

[VedantMadane]

Summary

Implements #276: slim tests/testIDT.cpp by removing redundant full-table literals.

Before: ~5.6k lines / ~400KB
After: ~800 lines / ~32KB

Approach

• Fixture loaders (camera SPST, illuminant, training data, CMF): assert structure + spot-check first/mid/last samples instead of embedding the entire JSON curve in C++.
• Transforms (scale LSC, TI, XYZ, RGB, chosen illuminants): keep a few sample OIIO_CHECK_EQUAL_THRESH values and assert a deterministic FNV-1a fingerprint over IEEE754 little-endian doubles for the full result.
• Left small 3-element WB/CM/IDT expected matrices as-is (already tiny).

Test plan

• Configure + build with usual rawtoaces_data dependency
• Run testIDT (or full unit test suite) on CI linux/mac/windows
• If a fingerprint mismatches only on a specific endian/FPU platform, document and adjust (hashes are LE double FNV-1a)

Closes #276

[linux-foundation-easycla]

• ❌ - login: @VedantMadane / name: Vedant Madane. The commit (ec2d1a9) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please visit our EasyCLA portal and chat with our support bot.