feat(fs/unstable): add rename

[jbronder]

This PR adds the rename API to @std/fs, which is intended to mirror Deno.rename function.

Towards #6255.

[codecov]

Codecov Report

Attention: Patch coverage is 61.11111% with 7 lines in your changes missing coverage. Please review.

Project coverage is 96.23%. Comparing base (1f032bb) to head (a73af8b).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
fs/unstable_rename.ts	61.11%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6379      +/-   ##
==========================================
- Coverage   96.24%   96.23%   -0.02%     
==========================================
  Files         555      556       +1     
  Lines       42047    42065      +18     
  Branches     6369     6371       +2     
==========================================
+ Hits        40470    40481      +11     
- Misses       1537     1544       +7     
  Partials       40       40              

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[kt3k]

LGTM. Thanks @jbronder !