Bound Bun.serve static-response stress memory

Context

The complete Home gate was nondeterministically OS-killed while the untouched Bun static-response stress matrix repeatedly materialized immutable 4 MiB route bodies. The upstream request counts, concurrency, methods, and assertions must remain unchanged.

Parent tracker: #66

Completed scope

• Cache immutable static-route arrayBuffer, blob, bytes, and text conversions on the original 200 GET response.
• Preserve per-response body-used semantics.
• Preserve Blob backing representation and content type.
• Exclude HEAD, redirects, 304, ranges, errors, and other non-200 responses from the cache.
• Pass untouched bun-serve-static.test.ts at 34 passed / 0 failed / 0 unsupported / 0 TODO with the full stress load.
• Complete the full home_test gate with exit code 0.

Completed on main in 4b1c17e.

The harness now reuses immutable static-route conversions only for 200 GET responses while preserving body-used checks and excluding HEAD/304/range/error paths.

Verification:

• untouched js/bun/http/bun-serve-static.test.ts: 34 passed / 0 failed / 0 unsupported / 0 TODO with all original batches and iterations
• untouched js/bun/http/bun-serve-file.test.ts: 66 passed / 0 failed / 0 unsupported / 2 upstream TODO
• full loopback-enabled home_test gate: exit code 0