Allows to annotate instance as delegate

[sobolevn]

Closes #265
Closes #263

[codecov-commenter]

Codecov Report

Merging #266 (90f30a4) into master (9e300d7) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #266   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines          101        99    -2     
  Branches        16        16           
=========================================
- Hits           101        99    -2     

Impacted Files	Coverage Δ
classes/_registry.py	100.00% <100.00%> (ø)
classes/_typeclass.py	100.00% <100.00%> (ø)

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