feat(opfs): implement missing OPFS features and add tests

[jurerotar]

• Compare handles by identity (same underlying entry), not by name/kind.
• Add queryPermission() and requestPermission() on file and directory handles; always resolve to "granted".
• getFile() returns snapshots with lastModified set; snapshots remain immutable after subsequent writes.
• Use a real WritableStream sink so both stream.write() and stream.getWriter().write() modify file content.
• Support all createWritable write() variants: raw USVString/Blob/ArrayBuffer/ArrayBufferView.
• Support all createWritable write() variants: { type: 'write', data, position? }.
• Support all createWritable write() variants: { type: 'seek', position }.
• Support all createWritable write() variants: { type: 'truncate', size }.
• Validate write/seek/truncate parameters: negative truncate size -> TypeError (write-params) / DOMException('IndexSizeError') (truncate method).
• Validate write/seek parameters: negative position -> TypeError; stream.seek(-1) -> DOMException('IndexSizeError').
• Reject undefined data with TypeError.
• Ensure binary correctness for Blob using arrayBuffer() (no text coercion).
• Preserve and expose seek()/truncate() methods on the returned writable stream.
• Abort semantics: abort(reason) causes subsequent write() to reject with the reason; close() rejects with a standardized errored-state message.
• createSyncAccessHandle: enforce exclusive file lock; opening a second handle throws InvalidStateError until the first is closed.
• createSyncAccessHandle: closed-state errors for getSize/read/write/truncate/flush throw DOMException('InvalidStateError').
• createSyncAccessHandle: read() at or beyond EOF returns 0; writes grow and pad file as needed; truncate() grows/shrinks and updates lastModified.
• Directory semantics: getFileHandle/getDirectoryHandle throw TypeMismatchError if opposite kind exists with same name.
• Directory removeEntry: deleting a file succeeds (regardless of recursive flag).
• Directory removeEntry: deleting an empty directory without recursive succeeds.
• Directory removeEntry: deleting a non-empty directory without recursive throws InvalidModificationError.
• Directory removeEntry: missing entry throws NotFoundError.
• Directory iteration APIs (entries/keys/values/[Symbol.asyncIterator]) yield consistent sets.
• Normalize DOMException creation to new DOMException(message, name) with standard names/messages.
• Add ambient declarations for queryPermission/requestPermission on FileSystemFileHandle and FileSystemDirectoryHandle.
• Tests: writable stream lifecycle and error paths, including getWriter().write() and getWriter().close().
• Tests: createWritable({ keepExistingData: true }) appends at end and persists content.
• Tests: abort semantics — write() rejects with reason; close() rejects with errored-state message; stream.write(undefined) rejects with TypeError.
• Tests: write() parameter variants and validation (seek/write/truncate; negative sizes/positions; legacy { data, position } and invalid data types).
• Tests: Blob binary correctness; DataView offset/length writes.
• Tests: sync handle exclusive lock, closed-state errors, flush() resolves when open, EOF reads return 0, growth/padding/truncation behaviors.
• Tests: directory and resolve semantics — NotFoundError for missing handles; name-clash TypeMismatchError; empty directory iteration; positive and negative resolve() cases.
• Tests: identity stability for navigator.storage.getDirectory() within a session; identity changes after resetMockOPFS().
• Tests: StorageManager.estimate() aggregates base usage and computed sizes.