Add uid/gid fields to FsStat and name resolution callbacks for ls/stat

[deathbyknowledge]

First off, this is an awesome project!

I have a custom IFileSystem implementation that has its own file ownership. Currently ls -l hardcodes user user and stat hardcodes 1000/user, making the ownership invisible. I've tried fixing this in a backwards compatible way, happy to amend as necessary.

• Added optional uid and gid fields to FsStat interface
• Added uidToName/gidToName callback options to BashOptions for resolving numeric IDs to names
• ls -l now uses real stat.mode via formatMode() instead of hardcoding drwxr-xr-x/-rw-r--r--
• ls -l resolves owner/group names from stat.uid/stat.gid using callbacks (falls back to "user"/"group")
• stat -c format specifiers %u, %U, %g, %G use real stat values + name resolution
• All changes are backwards-compatible (undefined uid/gid defaults to 1000, missing callbacks default to "user"/"group")

[vercel]

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