Make TreeSequence.samples args kw only

[benjeffery]

Fixes #1715

[codecov]

Codecov Report

Merging #1831 (cccddfb) into main (039dca0) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head cccddfb differs from pull request most recent head fb66eac. Consider uploading reports for the commit fb66eac to get more accurate results

@@            Coverage Diff             @@
##             main    #1831      +/-   ##
==========================================
- Coverage   93.39%   93.39%   -0.01%     
==========================================
  Files          27       27              
  Lines       24818    24814       -4     
  Branches     1094     1094              
==========================================
- Hits        23179    23175       -4     
  Misses       1604     1604              
  Partials       35       35              

Flag	Coverage Δ
c-tests	92.12% <ø> (ø)
lwt-tests	89.14% <ø> (ø)
python-c-tests	94.53% <100.00%> (-0.01%)	⬇️
python-tests	98.75% <100.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
python/tskit/trees.py	97.83% <100.00%> (ø)
python/tskit/metadata.py	98.84% <0.00%> (-0.01%)	⬇️
python/tskit/exceptions.py	100.00% <0.00%> (ø)

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[jeromekelleher]

LGTM. Nice to have a rudimentary test somewhere, though.

[benjeffery]

Test added and set to merge.