feat(encoding): compose generic block codecs

[Xuanwo]

Stack 4 of 10 for Lance generic block sequence compression.

This composes constant, bitpacking, RLE, range, delta, and dictionary codecs into a bounded u32/u64 cascade. Each concrete codec still owns its descriptor and payload contract; the cascade only evaluates complete serialized cost and chooses a strictly smaller valid candidate.

The layer completes the reusable codec set without adopting it in the variable-width writer. Stable Lance 2.0–2.2 bytes, selection, and reader behavior remain unchanged.

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• Position: 4 of 10
• Root: refactor(encoding): align block codecs with miniblock #8324
• Previous: feat(encoding): add bounded block dictionary #8326
• Next: fix(encoding): validate block bitpacking payloads #8328
• Top: perf(encoding): measure compressed mini-block offsets #8333