feat: Implement generic mechanism for layout_() modifiers

[Copilot]

• Analyze current modifier implementation and identify limitations
• Design generic modifier mechanism with apply functions
• Update layout_modifier() to support apply function
• Update component_wise() and normalize() to use new mechanism
• Refactor layout_() to use generic modifier application
• Add tests for the new generic modifier mechanism
• Update documentation
• Run full test suite to verify no regressions
• Address all code review feedback
• Export layout_modifier() so examples work correctly
• Clean up build artifacts
• Merge latest changes from main
• Run devtools::check() per updated AGENTS.md - all checks pass

Original prompt

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This section details on the original issue you should resolve

<issue_title>Implement better, generic mechanism for modifiers in layout.R</issue_title>
<issue_description>

rigraph/R/layout.R

Line 269 in 3e688cb

## TODO: better, generic mechanism for modifiers

@szhorvat please add any comment you have on what this should entail in practice.</issue_description>

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

• Fixes Implement better, generic mechanism for modifiers in layout.R #1473

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[krlmlr]

Can't comment.

[schochastics]

LGTM

[krlmlr]

@copilot: Run devtools::run_examples() and fix.

[Copilot]

@copilot: Run devtools::run_examples() and fix.

Fixed in commits 019d185 and 9c6a2ce. Exported layout_modifier() with proper documentation so the custom modifier examples in the documentation now work correctly. All examples now pass.

[krlmlr]

@copilot: Merge main and follow updated AGENTS.md .

[Copilot]

@copilot: Merge main and follow updated AGENTS.md .

Done in commit 4cb4894. Merged latest main branch and ran devtools::check() as per updated AGENTS.md. All checks pass with 0 errors, 0 warnings, 0 notes.

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