Cleanup uneeded duplication and move table metadata functions to mixins

[benjeffery]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 98.71795% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.82%. Comparing base (99f03e2) to head (576fde3).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
python/tskit/metadata.py	97.36%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3287      +/-   ##
==========================================
- Coverage   89.84%   89.82%   -0.02%     
==========================================
  Files          29       29              
  Lines       32719    32665      -54     
  Branches     5988     5982       -6     
==========================================
- Hits        29396    29342      -54     
  Misses       1882     1882              
  Partials     1441     1441              

Flag	Coverage Δ
c-tests	86.86% <ø> (ø)
lwt-tests	80.38% <ø> (ø)
python-c-tests	88.40% <ø> (ø)
python-tests	98.76% <98.71%> (-0.01%)	⬇️
python-tests-no-jit	33.18% <28.20%> (+0.13%)	⬆️
python-tests-numpy1	50.84% <30.76%> (+0.27%)	⬆️

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Files with missing lines	Coverage Δ
python/tskit/tables.py	99.29% <100.00%> (+0.03%)	⬆️
python/tskit/metadata.py	98.89% <97.36%> (-0.12%)	⬇️

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[jeromekelleher]

LGTM. I'm assuming this is all basically the same code except refactored into a mixin?

[benjeffery]

LGTM. I'm assuming this is all basically the same code except refactored into a mixin?

Yep