Port Bun subprocess pipe lifecycle leak matrices

Port the exact upstream spawn-pipe-leak.test.ts and spawn-pipe-read-error-leak.test.ts corpora into Home without TODO rewriting.

Scope:

• preserve buffered stdout when consumed before or after process exit
• release unread stdout ownership after process completion
• keep repeated subprocess batches memory-stable
• model injected PipeReader EBADF cleanup without leaked keep-alive state
• preserve platform skips for the Linux-only epoll scenario
• add durable Home regressions for both exact upstream files

Acceptance on macOS:

• corpora remain byte-identical to ~/Code/bun
• 4 passed, 0 failed, 0 unsupported, 0 todo
• adjacent spawn matrices remain green
• full home_test gate passes

Implemented and pushed in 3f406403daf6aff87b8d6fe3ac6b7bf009d0bf22.

Ported behavior:

• preserves logical stdout size and buffered content when consumed before or after process exit
• releases unread stdout ownership across repeated subprocess batches
• models large pipe payloads lazily so stress coverage does not manufacture allocation leaks
• models both injected PipeReader EBADF cleanup and the Linux dup2/epoll cleanup result
• removes both exact upstream files from Home TODO rewriting and adds a durable combined regression

Verification:

• both corpus files are byte-identical to ~/Code/bun
• spawn-pipe-leak.test.ts: 3 passed, 0 failed, 0 unsupported, 0 todo, with 0% RSS growth
• spawn-pipe-read-error-leak.test.ts: 1 passed, 0 failed, 0 unsupported, 1 upstream Linux-only platform skip on macOS
• adjacent package-script IPC regression: 1 passed, 0 failed, 0 unsupported, 0 todo
• ./pantry/.bin/zig build test -Dfilter=home_test --summary failures: exit 0

The issue acceptance said zero TODOs; on macOS the unchanged upstream file intentionally registers its Linux epoll test through test.skipIf(!isLinux), which the Home summary reports as one TODO. The cross-platform injected error path executes and passes.