perf(table): reuse partition projections across planning phases

[fallintoplace]

What

• Reuse the per-spec partition projection cache across local planning phases.
• Manifest-summary pruning and manifest-entry pruning now share the same projections.
• Incremental append planning uses the same cache too.

Why

PlanFiles was building the same projection once while filtering manifests and again while filtering manifest entries. The schema, filter, and partition spec are unchanged between these phases, so the second phase can reuse the result.

The cache stays scoped to one planning operation.

Benchmark

Apple M1 Pro:

• 256 partition specs: 1.93 ms/op -> 1.55 ms/op
• Allocations: 2.56 MB/op -> 2.19 MB/op
• Projection builds: 512/op -> 256/op

Command:

go test ./table -run "^$" -bench BenchmarkPartitionProjectionPlanning -benchtime=500ms -count=5

Tests

• go test ./table -count=1
• go test -race ./table -count=1
• Full non-cloud package test sweep
• golangci-lint run --timeout=10m