fix(fs): accept exts without leading period in walk[Sync]()

[iuioiua]

Previously, walk[Sync]() would return files and folders ending with strings, as defined in the exts option. E.g. It'd return the asserts folder when setting exts: ["ts"]. This is unexpected behaviour, as one would not expect folders to be turned when setting file extensions.

This change adds the leading period, ., to any extensions defined in exts, if missing, as there doesn't appear to be any good reason to require the user to have this leading period.

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.82%. Comparing base (b6906a9) to head (7760e94).

Files	Patch %	Lines
fs/walk.ts	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5345      +/-   ##
==========================================
- Coverage   95.82%   95.82%   -0.01%     
==========================================
  Files         458      458              
  Lines       37853    37859       +6     
  Branches     5563     5567       +4     
==========================================
+ Hits        36272    36277       +5     
- Misses       1541     1542       +1     
  Partials       40       40              

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[kt3k]

LGTM