fix(plots): apply labels without deprecated relabel helpers

[anevolbap]

Summary

Finishes the deprecation of the relabel helpers in pyfixest/report/utils.py (#1123). Each warning now names the function that was called (all said _relabel_expvar before), and _check_label_keys_in_covars warns too.

iplot() and coefplot() no longer call these helpers. On master both ignored labels unless cat_template was set, and emitted one DeprecationWarning per coefficient. labels now matches full coefficient names or each variable of an interaction term, without splitting variable::value names. iplot(cat_template=...) is deprecated: i() coefficients are already named variable::value, so the template never matched. Docs examples drop cat_template and rename_event_study_coefs(), which had no effect on these plots.

Verification

Passed on 393a866 (master merged in): pixi run -e py312 test-py (5792 passed, 336 s); pytest tests/test_plots.py tests/test_visualize.py tests/test_decomposition.py with extended tests (869 passed, 210 s); pixi run ty; prek run ruff-format and ruff-check on changed files; git diff --check. The new tests fail on master.

Deferred to exact-head CI (ci-tests.yaml, waiting for workflow approval): tests/test_did.py, which needs rpy2 and is not in the local py312 env, and docs-render for the changed iplot docstring and docs pages.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 95.23810% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pyfixest/report/visualize.py	95.00%	1 Missing ⚠️

Flag	Coverage Δ
core-tests	80.58% <95.23%> (+0.06%)	⬆️
test-r-core-other	48.43% <28.57%> (-0.02%)	⬇️
test-r-extended	23.01% <28.57%> (+0.02%)	⬆️
test-r-fixest	?
tests-extended	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
pyfixest/report/utils.py	96.42% <100.00%> (-1.17%)	⬇️
pyfixest/report/visualize.py	88.70% <95.00%> (-6.92%)	⬇️

... and 5 files with indirect coverage changes

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[s3alfisc]

Hi @anevolbap, thanks so much for the PR! Is it ready for a review from my side? It seems so at a first glimpse =)

[anevolbap]

Hi @anevolbap, thanks so much for the PR! Is it ready for a review from my side? It seems so at a first glimpse =)

Now it is, thanks!