feat(encoding): select bounded offset codecs

[Xuanwo]

Stack 6 of the Generic Block Sequence Compression series.

Depends on #8043.

This layer adds the adopter-private bounded offset statistics, candidate planning, and complete wire-cost comparison used to choose a reusable concrete block compressor for independent u32/u64 offset chunks. Candidates cover Constant, Range, Delta, Flat/bitpacking, RLE, Dictionary, and configured general compression. Losing candidates do not materialize payloads.

The selector remains test-only in this layer, so production mini-block writers and persisted bytes are unchanged. The next stack layer enables it only for eligible Lance 2.3 variable-width mini-block offsets.

Validation:

• cargo check -p lance-encoding --no-default-features --tests
• cargo check -p lance-encoding --tests --benches
• cargo test -p lance-encoding compression::tests
• cargo test -p lance-encoding encodings::physical
• cargo clippy --all --tests --benches -- -D warnings
• cargo fmt --all

Stack navigation

• Umbrella / integration reference: feat(encoding): add generic block compression #8002
• Previous: feat(encoding): add bounded block dictionary #8043
• Next: feat(encoding): encode generic mini-block offsets #8045