Add table extend method

[benjeffery]

Fixes #1271

[codecov]

Codecov Report

Merging #1287 (5a763d5) into main (6782342) will decrease coverage by 0.01%.
The diff coverage is 77.77%.

❗ Current head 5a763d5 differs from pull request most recent head 0755ba5. Consider uploading reports for the commit 0755ba5 to get more accurate results

@@            Coverage Diff             @@
##             main    #1287      +/-   ##
==========================================
- Coverage   93.84%   93.83%   -0.02%     
==========================================
  Files          26       26              
  Lines       22057    22073      +16     
  Branches     1006     1005       -1     
==========================================
+ Hits        20700    20712      +12     
- Misses       1324     1328       +4     
  Partials       33       33              

Flag	Coverage Δ
c-tests	92.47% <77.77%> (-0.03%)	⬇️
lwt-tests	92.97% <ø> (ø)
python-c-tests	95.14% <ø> (-0.01%)	⬇️
python-tests	98.86% <ø> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
c/tskit/tables.c	90.89% <77.77%> (-0.04%)	⬇️
python/tskit/trees.py	97.89% <0.00%> (-0.01%)	⬇️

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[jeromekelleher]

Looks good! I think we should tweak the semantics around num_rows though.

[benjeffery]

OK, changes made, will crack on with the other tables.

[benjeffery]

@jeromekelleher Should be good to go!

[jeromekelleher]

Really nice, thanks @benjeffery. One minor simplification we can make.