Introduce arrow, dtplyr, duckplyr-stingy, duckplyr-lavish backends

[Copilot]

• Add arrow, dtplyr, duckplyr as suggested dependencies in DESCRIPTION
• Add test_src_arrow(), test_src_dtplyr(), test_src_duckplyr_stingy(), test_src_duckplyr_lavish() in helper-config-db.R
• Update is_db_test_src() and copy_to_my_test_src() in helper-src.R to handle new backends
• Create test-arrow.R, test-dtplyr.R, test-duckplyr-stingy.R, test-duckplyr-lavish.R with dummy snapshot tests
• Update .github/versions-matrix.R to include new backends in CI matrix
• Run tests for each new backend (duckplyr_lavish: 19 failures, duckplyr_stingy: 64, arrow: 222, dtplyr: 248)
• Add skip_if_src() calls to failing tests (296 unique test locations processed)
• Some test locations (~30) could not be auto-matched to test_that() blocks due to non-standard line offsets — these need manual review and may still fail in CI
• Re-run tests to validate all skips are correctly placed
• Final code review and security scan

Original prompt

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This section details on the original issue you should resolve

<issue_title>Introduce new backends</issue_title>
<issue_description>Snake or kebab case, whatever works better. Add as a suggested dependency. Mirror all tests for existing database backends, skip tests that are currently failing. Create a patch that updates GitHub Actions for me to apply.

• arrow
• dtplyr
• duckplyr-stingy
• duckplyr-lavish</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Introduce new backends #2411

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[krlmlr]

@copilot: Run tests for each new backend. Add backend-specific skips as necessary for the failing tests.

[Copilot]

@copilot: Run tests for each new backend. Add backend-specific skips as necessary for the failing tests.

I ran tests for all 4 backends and identified failures: duckplyr_lavish (19), duckplyr_stingy (64), arrow (222), dtplyr (248). I generated skip_if_src() insertions for 296 unique failing test locations, but hit a rebase conflict pushing the changes — the branch has diverged from remote. The skip insertions need to be re-applied after reconciling the branch, and ~30 test locations with non-standard formatting need manual placement.

[krlmlr]

@copilot: Try again.

[krlmlr]

Too big, doing it in sub-issues.