Multiple open `Handle`s for the same file don't share metadata

[james-pre]

Multiple open Handles for the same file don't share metadata, meaning the inode can get out of sync.

Repro:

import * as fs from '@zenfs/core/promises'; // more readable

await fs.writeFile('example.txt', 'Hello World');

const a = fs.open('example.txt', 'r+');
const b = fs.open('example.txt', 'r+');

await a.truncate(5); // Contents are now "Hello"
const { size } = await b.stat();
assert.equal(size, 5); // fails because `b` doesn't have the updated metadata from `a`

The fix for this is to have Handles share their inode via a semi-global cache, which can be keyed using the FS' uuid and the file's ino.