fix: resolve ResourceWarning from unclosed file handles in validate and import (fixes #116)

[KmoM88]

Basic Info

The commands vcs validate and vcs import used argparse.FileType('r') which opens files at parse-time but doesn't provide a way to close them, resulting in unclosed file handle warnings.

This PR replaces argparse.FileType with string path arguments and explicitly manages the file descriptors using context managers for files, standard input, and URL streams.

Info	Please fill out this column
Ticket(s) this addresses	resolves #116
Primary OS tested on	Ubuntu
Is this a breaking change?	No
Does this PR contain AI generated software?	Yes

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Description of contribution in a few bullet points

• Replaced argparse.FileType with string arguments: Avoids opening files at argument parse time, preventing automatic file handle leaks.
• Implemented Context Managers: Ensures that local input files and remote URL streams are closed deterministically immediately after they are read.
• Maintained Backwards Compatibility: Added explicit handling for stdin (-) to preserve standard pipe-input workflows without closing the system's stdin stream.

Description of how this change was tested

1. Clone repository and create a Test File:

   • Create a file named example.repos with the following content:

     repositories:
       foo:
         type: git
         url: https://example.com/foo.git
         version: main

2. Reproduce the Warning (on main branch):

   • Run the validate command with warnings enabled:

     PYTHONWARNINGS=default vcs validate --input example.repos --retry 0

   • You should see a ResourceWarning: unclosed file in the output.

3. Verify the Fix (on fix/resource-warning-FileType branch):

   • Run the same command again:

     PYTHONWARNINGS=default vcs validate --input example.repos --retry 0

   • Expected: The command runs without any ResourceWarning.
   • Verify with the import command and with stdin as well:

     PYTHONWARNINGS=default vcs import --input example.repos --retry 0
     cat example.repos | PYTHONWARNINGS=default vcs validate --input - --retry 0
     cat example.repos | PYTHONWARNINGS=default vcs import --input - --retry 0

   • Expected: No warnings are shown for any of the commands.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 40.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 37.46%. Comparing base (fbd0321) to head (b8cff21).

Files with missing lines	Patch %	Lines
vcs2l/commands/import_.py	33.33%	5 Missing and 1 partial ⚠️
vcs2l/commands/validate.py	50.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #121       +/-   ##
===========================================
+ Coverage   26.76%   37.46%   +10.70%     
===========================================
  Files          31       31               
  Lines        2298     2306        +8     
  Branches      405      407        +2     
===========================================
+ Hits          615      864      +249     
+ Misses       1623     1334      -289     
- Partials       60      108       +48     

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[Copilot]

Pull request overview

Prevents file-handle leaks when validating or importing repository definitions.

Changes:

• Defers opening input paths until command execution.
• Closes local files and URL streams with context managers.
• Adds direct command invocation tests.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
vcs2l/commands/validate.py	Manages validation input streams explicitly.
vcs2l/commands/import_.py	Manages file and URL input streams explicitly.
test/test_commands.py	Adds direct invocation coverage.

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