feat: Support environment variables modifications

[jjerphan]

Description

Fix #1881.
Fix #4009.

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 0% with 116 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.30%. Comparing base (4a43769) to head (056ba37).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
libmamba/src/api/env.cpp	0.00%	54 Missing ⚠️
micromamba/src/env.cpp	0.00%	46 Missing ⚠️
libmamba/src/api/install.cpp	0.00%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4106      +/-   ##
==========================================
- Coverage   63.48%   63.30%   -0.18%     
==========================================
  Files         315      315              
  Lines       38644    38751     +107     
  Branches     2969     2980      +11     
==========================================
  Hits        24532    24532              
- Misses      14043    14150     +107     
  Partials       69       69              

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[jjerphan]

Comments for reviewers.

[Klaim]

LGTM, all my remarks are nitpicks, nothing important 👍🏽