feat(derive): Add pre_source hook

[andoriyu]

No description provided.

[codecov]

Codecov Report

Merging #19 into master will increase coverage by 0.72%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #19      +/-   ##
==========================================
+ Coverage   76.55%   77.28%   +0.72%     
==========================================
  Files          11       11              
  Lines         964      964              
==========================================
+ Hits          738      745       +7     
+ Misses        226      219       -7     

Impacted Files	Coverage Δ
src/lib.rs	100.00% <ø> (ø)
src/raw/object.rs	58.38% <0.00%> (+2.17%)	⬆️

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