compute: split index peek literal constraints per worker

[antiguru]

Summary

• Route index peek literal constraints to only the worker whose arrangement shard holds the key (row.hashed() % peers), instead of broadcasting all constraints to all workers
• Workers with no matching constraints short-circuit immediately with an empty response, avoiding trace clones, compaction setup, and cursor seeks

Known limitation: errors in arrangements are not sharded by key, so workers that receive no constraints may miss errors. This PR is for performance exploration only.

Test plan

• cargo check -p mz-compute
• cargo clippy -p mz-compute -p mz-compute-client
• cargo test -p mz-compute-client
• bin/sqllogictest -- test/sqllogictest/transform/literal_constraints.slt
• bin/sqllogictest -- test/sqllogictest/transform/notice/index_too_wide_for_literal_constraints.slt
• bin/sqllogictest -- test/sqllogictest/indexes.slt

🤖 Generated with Claude Code

[github-actions]

Pre-merge checklist

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