docs: add ClarkLDF doctest examples

[EKtheSage]

Summary: Add focused ClarkLDF Sphinx doctest examples and make the numeric comparison robust to small platform/dependency drift by rounding the displayed LDF values. Split from the larger #786 work and intentionally excludes .github/workflows/sync-main-to-docs.yml. Refs #704

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Note

Low Risk
Low risk: changes are limited to documentation/doctest additions and do not modify model logic or data handling.

Overview
Adds Sphinx doctest Examples to the ClarkLDF docstring covering (1) comparing loglogistic vs weibull growth curves, (2) using sample_weight to trigger the Cape Cod method and expose elr_, and (3) fitting with groupby to pool sparse segments.

The doctests round printed numeric outputs to reduce platform/dependency drift in rendered docs and CI doctest runs.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.23%. Comparing base (72b270c) to head (9fc573e).

Additional details and impacted files

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##             main     #802   +/-   ##
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  Coverage   86.23%   86.23%           
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  Files          86       86           
  Lines        4947     4947           
  Branches      643      643           
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  Hits         4266     4266           
  Misses        484      484           
  Partials      197      197           

Flag	Coverage Δ
unittests	86.23% <ø> (ø)

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[henrydingliu]

i went back and read a few pages from the pandas doc. a lot of them starts with a description of what a user is looking to accomplish, then goes through the details. but if we take the most curt example docstring I found on pandas, which is the xs function, the basic flow is still "user goal" -> "code implementation", rather than "in depth description of a parameter" -> "code implementation". could we do something similar with our examples? so instead of explaining the parameter, describe an issue then offer the parameter as the solution.

[henrydingliu]

awkward phrasing. the intentionality of the user is to use cape cod. to use cape cod, the user can pass in a weight vector without additional parameters in the clarkldf transformer.

[henrydingliu]

the example text makes a claim about individual triangles being too sparse to fit. the actual code doesn't really make that apparent, or even show the results at all

[henrydingliu]

too close to be a worthy choice of an example