chore: add yapf config to pyproject.toml

[SauravMaheshkar]

This PR aims to drop the .style.yapf file in favour of pyproject.toml in order to have a more minimal project structure.

Reference: Following google/yapf#708, pyproject.toml support was added.

[codecov-commenter]

Codecov Report

Merging #230 (b08c1a2) into main (058ce10) will decrease coverage by 7.37%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #230      +/-   ##
==========================================
- Coverage   89.21%   81.84%   -7.38%     
==========================================
  Files          52       52              
  Lines        5315     5315              
  Branches      549      549              
==========================================
- Hits         4742     4350     -392     
- Misses        438      810     +372     
- Partials      135      155      +20     

Impacted Files	Coverage Δ
src/ott/solvers/linear/discrete_barycenter.py	20.73% <0.00%> (-65.86%)	⬇️
src/ott/tools/segment_sinkhorn.py	43.75% <0.00%> (-56.25%)	⬇️
src/ott/solvers/quadratic/gw_barycenter.py	30.47% <0.00%> (-53.34%)	⬇️
src/ott/problems/quadratic/gw_barycenter.py	28.18% <0.00%> (-44.55%)	⬇️
src/ott/geometry/segment.py	62.22% <0.00%> (-37.78%)	⬇️
src/ott/tools/sinkhorn_divergence.py	63.15% <0.00%> (-35.09%)	⬇️
src/ott/tools/soft_sort.py	69.90% <0.00%> (-25.25%)	⬇️
src/ott/geometry/pointcloud.py	71.09% <0.00%> (-14.46%)	⬇️
src/ott/geometry/graph.py	77.50% <0.00%> (-14.38%)	⬇️
src/ott/problems/linear/potentials.py	79.34% <0.00%> (-9.79%)	⬇️
... and 21 more

[michalk8]

LGTM, thanks!