Fix highest coefficient normalization in Chebyshev U transforms

[vera-rubin]

The default Chebyshev U transforms doubled the highest coefficient in the forward direction and halved it in the inverse direction. We now normalize that mode along each transformed dimension for both in-place and out-of-place calls. We added a regression for U₂ and ran the full test suite.

Fixes #272

— ChipLab

[MikaelSlevinsky]

If you push a commit to bump the version, we can register right after merge

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.47%. Comparing base (fc411c0) to head (621f33b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #273      +/-   ##
==========================================
- Coverage   77.48%   77.47%   -0.01%     
==========================================
  Files          17       17              
  Lines        3233     3246      +13     
==========================================
+ Hits         2505     2515      +10     
- Misses        728      731       +3     

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