Main's SR2SubIFD white balance (#575) already reads the A900's applied
levels (2688 / 1024 / 1024 / 1516, the same 2.625 / 1.480 gains), so the
hard-coded maker-note 0x0020 block at offset 188 is dropped. The centred
crop now goes through #580's recorded_size_crop (a `centred` flag, only
for the packed 12-bit layout); every other body keeps main's framing.
Adds the CC0 A900 sample to the corpus with checks for its white balance,
black level, bit depth and crop. RENDER_CACHE_VERSION 38.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>