Port Bun.serve static response stress matrix

Tracks the focused Bun parity tranche split from #66.

Scope:

• execute js/bun/http/bun-serve-static.test.ts without corpus suppression
• support buffered typed response bodies and Blob conversion paths
• expose native GC and the upstream fillRepeating harness helper
• keep large binary equality and assertion diagnostics bounded
• preserve normalized Headers equality while matching non-enumerable internal state

Acceptance:

• exact upstream corpus source remains byte-identical
• all 34 tests pass with zero failures, TODOs, or unsupported cases
• adjacent response/file and cross-runner matcher matrices remain green
• full home_test gate passes

Completed and pushed in 78380df (published on main via f3fbf9b).

Verification:

• js/bun/http/bun-serve-static.test.ts: 34 passed, 0 failed, 0 TODO, 0 unsupported
• exact Home/upstream corpus SHA-256: ab86e22c3f8f2cafd29571abd96cff3bfa00feb6b7dc12fb16744dcb4dbe7f16
• adjacent bun-serve-file.test.ts: 66 passed, 0 failed, 0 unsupported, 2 upstream TODOs
• adjacent body-clone.test.ts: 25 passed, 0 failed, 0 TODO, 0 unsupported
• cross-runner expect.test.js: 398 passed, 0 failed, 0 unsupported, 10 upstream TODOs
• complete home_test gate: 1,133 total, 1 skipped, 0 failed
• zig fmt --check and git diff --check: pass

The unrelated Undici Headers constructor-validation gap is tracked separately in #175.