feat: infer R argument parity (med, prop_test options, weighted sampling, …)

[ismayc]

Second of the two argument-parity PRs (companion to #18). Closes the remaining infer argument gaps; all functions already existed.

• hypothesize(med=) / observe(med=) — median point null (bootstrap shift centered on the median).
• prop_test(z=, correct=, conf_int=, conf_level=) — now mirrors R's prop.test: chi-square statistic by default (with a chisq_df column), z=True for the signed z, Yates continuity correction, and a confidence interval (Wilson score for one proportion; Wald + correction for a two-proportion difference). Validated numerically against R (X-squared, p-value, and CI all match).
• rep_slice_sample(prop=, weight_by=) and rep_sample_n(prob=) — fractional and weighted sampling.
• generate(variables=) — choose which column the permutation shuffles.
• shade_p_value/shade_confidence_interval(fill=) and visualize(dens_color=); shade_p_value now also honors color (it was previously ignored — a latent bug, now fixed).

Tests cover every new path, with prop_test and the correlation methods asserted against R-computed reference values. 296 tests, 100% coverage, ruff clean.

Behavior change: prop_test now defaults to the chi-square statistic (R parity) rather than a z; pass z=True for the old z-statistic.

Merge note: #18 and this PR both append to CHANGELOG.md; the second to merge will need a one-line conflict resolution (I'll handle it).

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (82c3afb) to head (a456fa2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #19   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           22        22           
  Lines         1422      1492   +70     
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+ Hits          1422      1492   +70     

Files with missing lines	Coverage Δ
moderndive/infer/core.py	100.00% <100.00%> (ø)
moderndive/infer/viz/__init__.py	100.00% <100.00%> (ø)
moderndive/infer/viz/_plotly.py	100.00% <100.00%> (ø)
moderndive/infer/viz/_plotnine.py	100.00% <100.00%> (ø)
moderndive/infer/wrappers.py	100.00% <100.00%> (ø)
moderndive/sampling.py	100.00% <100.00%> (ø)

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