WasmVM: VFS directory enumeration incomplete (readdir, seekdir, scandir, fdopendir)

[NathanFlurry]

Summary

WASI VFS directory enumeration functions are not fully implemented, causing os-test dirent and nftw tests to fail. The VFS needs to support fd_readdir properly so that libc functions like readdir(), rewinddir(), seekdir(), scandir(), and fdopendir() work correctly. nftw() (file tree walk) also depends on working directory enumeration.

Affected os-test cases

• basic/dirent/fdopendir
• basic/dirent/readdir
• basic/dirent/rewinddir
• basic/dirent/scandir
• basic/dirent/seekdir
• basic/ftw/nftw

Expected behavior

All dirent functions should enumerate directory contents correctly through the WASI VFS layer.

Context

Discovered via os-test POSIX conformance suite. Tracked in posix-exclusions.json as fail / implementation-gap.