Feat add uv-smooth algorithm

[samaloney]

• Working version
• Generalise
• Add option of Matern kernel
• Docs
• Test

[codecov]

Codecov Report

Attention: Patch coverage is 21.05263% with 75 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@670e48a). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
xrayvision/uv_smooth.py	6.25%	75 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #87   +/-   ##
=======================================
  Coverage        ?   82.46%           
=======================================
  Files           ?       10           
  Lines           ?     1032           
  Branches        ?        0           
=======================================
  Hits            ?      851           
  Misses          ?      181           
  Partials        ?        0           

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