feat: support copying from local file protocol

[pandanoir]

resolves #109

Support for the file protocol has been added.

• Templates can now be specified using file:///path/to/dir
• Tilde (~) expansion is also supported. However, since the standard file:// format typically only supports absolute paths, a custom format file:~/ is used to enable this feature.

Since the file protocol involves copying a directory rather than extracting a tarball, the processing logic and handling of options differ significantly from those in downloadTemplate. For this reason, we’ve separated the responsibilities and implemented it as a separate function.

If you believe it would be better to handle the file protocol as a branch within downloadTemplate, we’re happy to revise the implementation accordingly. We would appreciate your feedback.

[pandanoir]

@pi0
Gentle reminder: could you review this when you get a chance?

[codecov]

Codecov Report

❌ Patch coverage is 62.06897% with 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.52%. Comparing base (743c9ae) to head (7fbbdfc).
⚠️ Report is 70 commits behind head on main.

Files with missing lines	Patch %	Lines
src/cli.ts	0.00%	19 Missing ⚠️
src/giget.ts	73.58%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #228      +/-   ##
==========================================
- Coverage   54.63%   48.52%   -6.11%     
==========================================
  Files           7        6       -1     
  Lines         615      577      -38     
  Branches       47       62      +15     
==========================================
- Hits          336      280      -56     
- Misses        278      297      +19     
+ Partials        1        0       -1     

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