Allow user to specify the model statistics to be displayed as well as their order

[dsliwka]

Replaces the previously hard‑wired bottom panel model statistics logic in etable with more flexible system.

Key changes:

• New arguments: model_stats (list of attribute names without leading _) and model_stats_labels (optional label overrides).
• Any model attribute can be displayed by listing its name without "_" (e.g. _r2_within -> "r2_within", _N -> "N"). Should therefore also work with future estimation methods and attributes.
• Default (when model_stats=None) reproduces legacy behavior: ["N", "se_type?" if show_se_type, "r2", ("r2_within" if available else "adj_r2")].
• Passing an empty list model_stats=[] suppresses all built‑in stats.

Addresses #983.

[codecov]

Codecov Report

❌ Patch coverage is 90.14085% with 7 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pyfixest/report/summarize.py	90.14%	7 Missing ⚠️

Flag	Coverage Δ
core-tests	76.78% <90.14%> (?)
tests-extended	?
tests-vs-r	15.79% <2.81%> (-0.01%)	⬇️

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Files with missing lines	Coverage Δ
pyfixest/report/summarize.py	88.86% <90.14%> (+78.97%)	⬆️

... and 42 files with indirect coverage changes

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[dsliwka]

pre-commit.ci autofix

[s3alfisc]

Thank you Dirk, I'll try to take a look tomorrow (latest by Wednesday). Sorry for not replying earlier to your comments!