fix(file): accept absolute paths

[favonia]

Closes #172.

[codecov]

Codecov Report

Merging #173 (b27ac56) into main (2fa8268) will decrease coverage by 0.16%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main     #173      +/-   ##
==========================================
- Coverage   83.48%   83.31%   -0.17%     
==========================================
  Files          27       27              
  Lines        1568     1576       +8     
==========================================
+ Hits         1309     1313       +4     
- Misses        254      257       +3     
- Partials        5        6       +1     

Flag	Coverage Δ
unittests	83.31% <50.00%> (-0.17%)	⬇️

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Impacted Files	Coverage Δ
internal/file/file.go	73.33% <50.00%> (-26.67%)	⬇️

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