feat: add SimplifiableIfMatchViolation for single-case matches

[CommitToday]

Overview

This PR adds a new violation SimplifiableIfMatchViolation that flags single-case match statements that can be simplified to if statements. This helps reduce unnecessary complexity and cognitive load when a simple if condition would suffice.

Checklist

• [x] Code changes implemented
• [x] Tests added for new violation
• [x] Documentation included in violation docstring

Proof

The new violation is tested with various cases in test_simplified_match_conditions.py:

• Single-case matches with simple literals (e.g., case 1:, case True:, case "string":) trigger the violation
• Single-case matches with as-binding also trigger the violation
• Multi-case matches, matches with guards, wildcard cases, and complex patterns do not trigger the violation
• The violation correctly identifies when a single-case match can be simplified to an if statement

Closes #3528