feat: add callbacks

[codecov-commenter]

Codecov Report

Merging #343 (b51c1bf) into main (37df2d6) will decrease coverage by 1.48%. The diff coverage is 86.74%.

:exclamation: Current head b51c1bf differs from pull request most recent head ae2dad3. Consider uploading reports for the commit ae2dad3 to get more accurate results

@@            Coverage Diff             @@
##             main     #343      +/-   ##
==========================================
- Coverage   94.98%   93.50%   -1.49%     
==========================================
  Files          24       27       +3     
  Lines         479      539      +60     
==========================================
+ Hits          455      504      +49     
- Misses         24       35      +11     

Impacted Files	Coverage Δ
R/helper.R	63.15% <ø> (-1.85%)	:arrow_down:
R/ContextEval.R	44.44% <44.44%> (ø)
R/mlr_callbacks.R	96.87% <96.87%> (ø)
R/AutoTuner.R	95.23% <100.00%> (+0.05%)	:arrow_up:
R/CallbackTuning.R	100.00% <100.00%> (ø)
R/ObjectiveTuning.R	97.72% <100.00%> (+0.29%)	:arrow_up:
R/TuningInstanceMulticrit.R	100.00% <100.00%> (ø)
R/TuningInstanceSingleCrit.R	100.00% <100.00%> (ø)
R/auto_tuner.R	100.00% <100.00%> (ø)
R/tune.R	94.73% <100.00%> (ø)

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