Add h-transform for TI costs

[michalk8]

TODO:

• tests

[codecov]

Codecov Report

Attention: Patch coverage is 11.11111% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 90.93%. Comparing base (c37f0c4) to head (4dbd571).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #525      +/-   ##
==========================================
- Coverage   91.04%   90.93%   -0.11%     
==========================================
  Files          68       68              
  Lines        7054     7063       +9     
  Branches      998      998              
==========================================
+ Hits         6422     6423       +1     
- Misses        478      486       +8     
  Partials      154      154              

Files	Coverage Δ
src/ott/geometry/costs.py	90.95% <11.11%> (-1.66%)	⬇️

[marcocuturi]

LGTM, thanks!

Note for self: maybe we should also add an empty template method in geometries, to define the c_transform, overriding it with h_transform for TICosts

[marcocuturi]

(apologies, hadn't realized the tests were coming (>_<;)

please add them in another PR