fix: Solve bug when changing permissions with no modification right

[pkrog]

Description

When trying to set execution mode for a file or setting permissions to cache directory, an error may occur if we have no modification right on the parent folder.
This error occurs regardless of the current permissions on the targeted file or folder.
Thus, even if we already have the required permissions on the targeted file or folder, the error occurs.

This pull request introduces a function has_permissions() that tests if we already have the wanted permissions on a file or folder.
This new function is used at the two places described above, in order to avoid a useless setting of permissions that would lead to an error.

Type of Change

• Bugfix
• Feature / enhancement
• CI / Documentation
• Maintenance

Checklist

• My code follows the general style and conventions of the codebase, ensuring consistency
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have run pre-commit run --all locally in the source folder and confirmed that there are no linter errors.
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes

[codecov]

Codecov Report

❌ Patch coverage is 97.14286% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.63%. Comparing base (c641811) to head (ad237ab).

Files with missing lines	Patch %	Lines
libmamba/src/core/subdir_index.cpp	84.61%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4107      +/-   ##
==========================================
+ Coverage   63.58%   63.63%   +0.05%     
==========================================
  Files         315      315              
  Lines       38562    38621      +59     
  Branches     2950     2954       +4     
==========================================
+ Hits        24518    24578      +60     
+ Misses      13975    13974       -1     
  Partials       69       69              

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[pkrog]

Codecov Report

❌ Patch coverage is 97.14286% with 2 lines in your changes missing coverage. Please review. ✅ Project coverage is 63.63%. Comparing base (c641811) to head (ad237ab).
Files with missing lines Patch % Lines
libmamba/src/core/subdir_index.cpp 84.61% 2 Missing ⚠️
Additional details and impacted files

☔ View full report in Codecov by Sentry. 📢 Have feedback on the report? Share it here.
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Note that I am not responsible for the two lines in question. They were here before, thus already not tested.

[Klaim]

LGTM in essence but I would need a bit more documentation of the function.

As for the CI error on Windows, I'm not totally sure but I suspect the specific check is about a kind of permission not supported by that OS? Not sure.

[Klaim]

Could you add:

• a clarification that this function is not part of std::filesystem (mamba::fs namespace reflects std::filesystem, see the comment at the top of the file for why);
• clarifications on the preconditions, in particular what happens if the provided path doesnt lead to a file or directory;

[Klaim]

Why are these headers required if you're using only the C++ standard library api?