Group side effects in own class

[hanneskaeufler]

This makes the new cli commands nicer.

[codecov]

Codecov Report

Merging #69 into master will decrease coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #69      +/-   ##
==========================================
- Coverage   94.96%   94.93%   -0.04%     
==========================================
  Files          46       47       +1     
  Lines         636      632       -4     
==========================================
- Hits          604      600       -4     
  Misses         32       32

Impacted Files	Coverage Δ
src/crytic/side_effects.cr	100% <100%> (ø)
src/crytic/cli_options.cr	100% <100%> (ø)	⬆️

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