perf(table): elide identity partition filters

[fallintoplace]

What

• Elide identity partition predicates from local scan task residuals.
• Mixed filters keep only the remaining row predicate. Example: tenant_id = acme AND amount > 100 becomes amount > 100.
• Use the task residual for Arrow projection, so AlwaysTrue residuals do not read filter-only columns.
• Keep unknown partition values and transformed predicates conservative.
• This PR intentionally supports identity transforms only.

Why

Local scans already use task residuals while reading, but local planning left them nil. This made files re-evaluate predicates already proven by identity partition values.

Benchmark

Planning overhead

Command: go test ./table -run '^$' -bench '^BenchmarkPartitionResidualPlanning$' -benchmem -count=5

Apple M1 Pro:

• 0.866 to 0.897 ms/op for 4,096 files
• 425,984 B/op
• 16,384 allocs/op

This measures residual planning overhead only.

Arrow read path

Command: go test ./table -run '^$' -bench '^BenchmarkArrowScanTaskResidual$' -benchmem -count=5

Apple M1 Pro, 32,768-row Parquet file, projecting payload only:

• Identity-only filter, original filter: about 2.75 ms/op, 8.98 MB/op, 946 allocs/op
• Identity-only filter, AlwaysTrue residual: about 1.55 ms/op, 5.55 MB/op, 520 allocs/op
• Mixed filter, original filter: about 3.52 ms/op, 19.86 MB/op, 1,833 allocs/op
• Mixed filter, amount > 100 residual: about 3.02 ms/op, 17.33 MB/op, 1,488 allocs/op

The read benchmark compares the original filter path with the task residuals produced by this PR.

Checks

• go test ./table -count=1
• go test -race ./table -count=1
• /Users/hoangvu/go/bin/golangci-lint run ./table/... --timeout=5m