Feat/rust for percentiles

[Oisin-M]

Description

Tackles part of #147. Close #68.

Now have

ekh.upstream.percentile(river_network, field, p)
ekh.upstream.array.percentile(river_network, field, p)
ekh.catchments.percentile(river_network, field, p)
ekh.catchments.array.percentile(river_network, field, p)

Will not support weights in first version, nor will we support downstream.percentile. Switching return_type gridded or masked works out of the box.

Median is percentile with p=0.5, so this is trivial to add if we want a separate function.

Tasks:

• rust-accelerated percentile function (full field)
• (later PR) support weights
• (Optional) nan support
• ekh.upstream.percentile
• (later PR) ekh.downstream.percentile
• ekh.catchments.percentile
• assert using numpy
• array type handling (autoconvert to float64)
• ensure percentile requested is in [0,1].
• docs
• code clean-up
• tests

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.24%. Comparing base (1ae44bd) to head (e15acf7).
⚠️ Report is 13 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #156      +/-   ##
===========================================
+ Coverage    92.50%   94.24%   +1.74%     
===========================================
  Files            8       20      +12     
  Lines          200      278      +78     
===========================================
+ Hits           185      262      +77     
- Misses          15       16       +1     

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