[WIP] Replace conditionals in match with #:when

[Copilot]

• Explore repository structure and understand codebase
• Run existing tests to validate current state
• Analyze existing match-shortcuts and conditional-shortcuts patterns
• Implement new refactoring rule for converting match conditionals to #:when
• Add comprehensive tests for the new refactoring rule
• Basic rule works for multi-branch match expressions with simple patterns
• Fix rule to properly restrict to simple patterns only (complex nested patterns currently still match)
• Fix rule ordering to prevent single-clause matches from being converted incorrectly
• Validate rule works with both if and cond expressions
• Test edge cases and ensure minimal changes

The basic refactoring rule is working and correctly transforms conditionals in multi-clause match expressions to use #:when clauses. However, there are still two issues to resolve:

1. The rule currently matches complex nested patterns when it should only match simple ones
2. Single-clause matches are being transformed by the existing single-clause-to-match-define rule

Fixes #389.

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