fix: do not throw when fs is not extensible

[dyk1454683243-sudo]

Fixes #245

Bug

In ESM, import * as fs from 'node:fs' is a non-extensible namespace object. graceful-fs published the shared retry queue with Object.defineProperty(fs, Symbol.for('graceful-fs.queue'), …) and threw:

TypeError: Cannot define property Symbol(graceful-fs.queue), object is not extensible

Reproduced on current main by Object.preventExtensions(require('fs')) then require('graceful-fs').

Fix

• If fs (or global) is not extensible, skip defining the queue Symbol on that object instead of throwing.
• Keep the existing Symbol-on-fs publish path when Object.isExtensible(fs) is true, so CJS / multi-copy queue sharing is unchanged.
• When the Symbol cannot be stored on fs, use global[Symbol.for('graceful-fs.queue')] (already used for cross-version sharing) and a module-local array as fallbacks.
• Queue reads (enqueue / retry / resetQueue) go through getQueue() so the fallback is used.

This is a separate change from #262 (getter-only fs.close).

Tests

• test/non-extensible-fs.js: load this tree against a cloned, Object.preventExtensions fs-like object (nyc preloads node_modules/graceful-fs onto the real fs). Asserts load does not throw, file ops still work, the queue is not defined on the non-extensible object, later loads share the global queue, and EMFILE retries still drain that queue.
• test/queue-published-on-fs.js: extensible CJS fs still gets the Symbol and shares one array with global.

Local npm test: 49472 passing.

Claim-check

• TypeError: Cannot define property Symbol(graceful-fs.queue), object is not extensible #245 is still open
• closed_by_pull_requests.total_count was 0
• No open or closed PR used Fixes / Closes / Resolves TypeError: Cannot define property Symbol(graceful-fs.queue), object is not extensible #245
• No existing PR about non-extensible fs / ESM / Symbol(graceful-fs.queue)
• Does not modify fix: do not throw when fs.close is getter-only #262