git: implement remaining gto tag functions

[pmrowla]

adds more prerequisites from GTO around annotated tag behavior

[codecov-commenter]

Codecov Report

Patch coverage: 74.41% and project coverage change: -0.08% ⚠️

Comparison is base (8d591ce) 80.51% compared to head (b9c633e) 80.44%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #266      +/-   ##
==========================================
- Coverage   80.51%   80.44%   -0.08%     
==========================================
  Files          27       27              
  Lines        4199     4235      +36     
  Branches      741      748       +7     
==========================================
+ Hits         3381     3407      +26     
- Misses        685      694       +9     
- Partials      133      134       +1     

Files Changed	Coverage Δ
src/scmrepo/git/backend/dulwich/__init__.py	78.71% <53.84%> (-0.71%)	⬇️
src/scmrepo/git/backend/pygit2/__init__.py	75.86% <72.22%> (-0.08%)	⬇️
src/scmrepo/git/__init__.py	85.57% <100.00%> (+0.04%)	⬆️
src/scmrepo/git/backend/base.py	81.15% <100.00%> (ø)
src/scmrepo/git/backend/gitpython.py	65.56% <100.00%> (ø)
src/scmrepo/git/objects.py	74.40% <100.00%> (+1.75%)	⬆️

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