fix: patch all async fs methods (callback + promises) for VFS interception

[robertsLando]

Summary

The VFS module hooks only patched synchronous fs methods (readFileSync, statSync, existsSync, etc.), leaving all async operations unpatched. This caused ENOENT errors when application code used callback-based fs.* or fs.promises.* / require('fs/promises').* to access files inside the VFS.

Fixes #8

Patched methods

Sync (new):

• fs.accessSync
• fs.readlinkSync

Callback (new):

• fs.access
• fs.stat
• fs.lstat
• fs.readFile
• fs.readdir
• fs.readlink
• fs.realpath
• fs.createReadStream

Promises (new) — patched directly on fs.promises so require('fs/promises') also picks up the changes (same object reference):

• fs.promises.access
• fs.promises.readFile
• fs.promises.stat
• fs.promises.lstat
• fs.promises.readdir
• fs.promises.readlink
• fs.promises.realpath

Coverage matrix

Method	Sync	Callback	Promises
stat	✅ (existing)	✅ new	✅ new
lstat	✅ (existing)	✅ new	✅ new
readFile	✅ (existing)	✅ new	✅ new
readdir	✅ (existing)	✅ new	✅ new
readlink	✅ new	✅ new	✅ new
realpath	✅ (existing)	✅ new	✅ new
access	✅ new	✅ new	✅ new
existsSync	✅ (existing)	N/A (deprecated)	N/A
createReadStream	N/A	✅ new (stream)	N/A

Context

Discovered while testing yao-pkg/pkg SEA mode with a real-world application that uses:

• fs.stat(path, callback) via send module (used by express.static)
• await fs.promises.access(path, F_OK) for file existence checks
• await fs.promises.readFile(path) for loading HTML email templates
• fs.readdir / fs.realpath callbacks via glob and graceful-fs

All sync equivalents worked fine since they were already patched.

Test plan

• npm run lint passes
• npm test — 176/176 tests pass
• Callback patches deliver errors via process.nextTick (non-throwing)
• createReadStream returns a proper Readable for VFS files
• fs.realpath.native preserved as passthrough

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