fix(bitmap): align BITFIELD bit order with Redis

[maoyouaa]

Summary

• Align BITFIELD and BITFIELD_RO on bitmap keys with Redis bit ordering by reversing bits at the bitmap storage boundary.
• Use a fixed 9-byte stack buffer for bitmap-to-bitfield conversion.
• Add regression coverage for signed values, overflow modes, sparse bitmaps, missing data, and segment boundaries.

Root cause

Kvrocks bitmap segments store bits in LSB order, while BITFIELD interprets byte buffers in MSB order. The bitmap conversion path copied bytes directly, producing results inconsistent with Redis and with GET/GETBIT.

Compatibility

Bitmap values written by older versions through the incorrect BITFIELD path have no format marker and cannot be distinguished automatically. This change preserves the existing bitmap LSB storage format and fixes conversion at the BITFIELD boundary.

Validation

• Docker GCC build
• Go TestBitmap
• Redis 7 comparison for signed values, overflow behavior, and sparse reads
• clang-format, focused clang-tidy, and git diff --check

Closes #2500

[PragmaTwice]

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