[feat] add "env" context

[icepuma]

• reads environment variables and injects them into own context

[codecov-commenter]

Codecov Report

Merging #151 (34fde6e) into main (3a8e7e7) will increase coverage by 3.89%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #151      +/-   ##
==========================================
+ Coverage   48.79%   52.68%   +3.89%     
==========================================
  Files          47       48       +1     
  Lines        1863     1767      -96     
==========================================
+ Hits          909      931      +22     
+ Misses        954      836     -118     

Impacted Files	Coverage Δ
src/contexts/env.rs	100.00% <100.00%> (ø)
src/contexts/mod.rs	84.05% <100.00%> (+3.70%)	⬆️
src/actions/directory/mod.rs	0.00% <0.00%> (ø)
src/actions/package/providers/yay.rs	0.00% <0.00%> (ø)
src/actions/package/providers/bsdpkg.rs	0.00% <0.00%> (ø)
src/actions/package/providers/winget.rs	0.00% <0.00%> (ø)
src/actions/package/providers/homebrew.rs	0.00% <0.00%> (ø)
src/contexts/os.rs	96.42% <0.00%> (+0.13%)	⬆️
src/actions/file/copy.rs	14.06% <0.00%> (+0.42%)	⬆️
src/actions/file/link.rs	92.92% <0.00%> (+0.92%)	⬆️
... and 20 more

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