Reject writable file commands after close or abort

[wieslawsoltes]

Problem and result

The macOS 12 package CTest webscene_native_file_system_access reached FileSystemWritableFileStream.write() after a successful atomic close() and did not reject with TypeError. The direct write, seek, and truncate methods checked only stream identity before queuing into the generic WritableStream. They now reject when the native transaction has already been cleared by close or abort, without reopening or mutating the file.

Focused gate

The existing native File System Access fixture now checks all three commands after both close and abort, retaining the atomic commit and rollback byte assertions. git diff --check passes. Run the webscene_native_file_system_access CTest and related native runtime CI on this exact head before merge; the local V8/SDK build cache was removed during requested artifact cleanup. Full macOS package CTest failures in other subsystems remain tracked by #914.

Closes #915. Related owner: #248.

[wieslawsoltes]

Merge gate: exact head 01b8cd4 passed webscene_native_file_system_access in macOS package job 106649301824 (3.40s), plus macOS and Linux runtime CI and contracts. The package suite still has six unrelated failures tracked by #914; the File System Access failure from #915 is cleared.