Thread service levels through pebble lanes

[Osvaldo Andrade (osvaldoandrade)]

Summary

• add ctx-aware Pebble read/write APIs that resolve service-level lane shares from request context
• attach a catalog-backed service-level shares resolver to gRPC storage handles, with cache invalidation on service-level updates
• route gRPC item, batch, query, scan, transaction, MV, and GI write paths through the ctx-aware APIs
• re-enable the workload isolation latency test with lanes enabled in the fixture

Validation

• go test ./internal/storage/adapter/pebble
• go test ./internal/server
• go test ./internal/server/...
• go test ./...
• go test -race -count=1 ./internal/server ./internal/server/... ./internal/storage/adapter/pebble ./internal/catalog ./internal/auth
• go test ./internal/storage/adapter/pebble -run '^$' -bench 'Benchmark(RunReadNoOp|RunWriteNoOp|LaneDisabledVsEnabled|PutItem|GetItem)$' -benchtime=200ms
• go vet ./...
• go build ./...

Closes #550