perf(encoding): measure compressed mini-block offsets

[Xuanwo]

Stack 10 of 10 for Lance generic block sequence compression.

This adds representative Criterion workloads for v2.2 flat and v2.3 generic variable-width mini-block offsets. The harness records complete encoded bytes and measures encode, full scan, and cold/warm chunk-local take paths for range-friendly and delta-friendly corpora.

Benchmark

Measured at ae0a49ba2 with the release-with-debug profile over 262,144 UTF-8 rows.

Workload	Encoded bytes	Encode median	Scan median	Cold take median	Warm take median
Range, v2.2 → v2.3	5,283,840 → 4,218,880 (-20.2%)	1.512 → 6.824 ms	1.330 → 1.170 ms	249.2 → 202.3 µs	233.6 → 186.8 µs
Delta, v2.2 → v2.3	10,436,608 → 9,355,264 (-10.4%)	2.650 → 10.014 ms	2.136 → 2.259 ms	232.4 → 246.3 µs	219.2 → 226.4 µs

Stack navigation

• Position: 10 of 10
• Root: refactor(encoding): align block codecs with miniblock #8324
• Previous: docs(format): define generic mini-block offsets #8332
• Next: none
• Top: perf(encoding): measure compressed mini-block offsets #8333

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