Migrate R snapshot tests to pytest-r-snapshot

[nanxstats]

Fixes #180

This PR migrates the R snapshot tests from the previous ad-hoc code extraction, snapshot saving, and comparison logic, to using the new package pytest-r-snapshot instead.

• Switch RTF snapshot assertions to r_snapshot with semantic normalization.
• Add missing R code chunk labels for footnote/source snapshots.
• The snapshots are saved under the default location tests/__r_snapshots__/.

[Copilot]

Pull request overview

This PR successfully migrates the R snapshot testing infrastructure from a custom ad-hoc implementation to the standardized pytest-r-snapshot package, addressing issue #180. The migration eliminates manual fixture generation and comparison logic, replacing it with a cleaner, more maintainable approach.

Key changes:

• Replaces custom ROutputReader class and fixture generation script with pytest-r-snapshot package
• Consolidates RTF normalization logic into reusable normalize_rtf_semantic() function
• Adds missing R code chunk labels for footnote and source snapshot tests

Reviewed changes

Copilot reviewed 36 out of 40 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
uv.lock	Adds pytest-r-snapshot==0.1.0 dependency with package metadata and hashes
pyproject.toml	Includes pytest-r-snapshot>=0.1.0 in dev dependencies
.github/workflows/ci-tests.yml	Installs pytest-r-snapshot in CI test workflows
.github/workflows/mkdocs.yml	Installs pytest-r-snapshot in documentation build workflow
tests/utils.py	Removes deprecated ROutputReader class (15 lines deleted)
tests/utils_snapshot.py	Adds normalize_rtf_semantic() function to consolidate normalization steps; refactors assert_rtf_equals_semantic() to use it
tests/test_single_page_rtf.py	Migrates 16 tests to use r_snapshot fixture with semantic normalization
tests/test_row.py	Migrates 3 tests to use r_snapshot fixture
tests/test_pagination.py	Migrates 1 test to use r_snapshot fixture
tests/test_input.py	Migrates 5 tests to use r_snapshot fixture; adds R code chunk labels for footnote and source snapshot tests
tests/fixtures/run_r_tests.py	Removes entire fixture generation script (127 lines)
tests/fixtures/README.md	Removes fixture documentation (no longer needed)
tests/fixtures/r_outputs/*	Removes old manually-generated snapshot files
tests/__r_snapshots__/**/*.rtf	Adds new snapshot files generated by pytest-r-snapshot with updated font charset values

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