Add substring filtering support for TypeSpec integration test generation

[Copilot]

This PR enhances the --filter option in TypeSpec integration test generation commands to support partial/substring matching, making it much easier to generate specific subsets of test cases.

Problem

Previously, the --filter option only supported exact path matching. To generate test cases, you had to know the exact outputPath of each test case, which made it difficult to generate related groups of tests. For example, there was no easy way to generate all authentication-related tests or all type-related tests.

Solution

Enhanced the filtering logic in gen-cadl-ranch.js to support three matching strategies:

1. Exact match (unchanged for backward compatibility): tsp.outputPath === pathFilter
2. Substring match in outputPath: tsp.outputPath.includes(pathFilter)
3. Substring match in inputPath: tsp.inputPath.includes(pathFilter)

Usage Examples

Now you can use intuitive filter keywords to generate related test cases:

# Generate all type-related specs (type/array, type/dictionary, type/union, etc.)
npm run generate-tsp-only:rlc --filter=type

# Generate all authentication-related specs
npm run generate-tsp-only:rlc --filter=authentication

# Generate all server-related specs  
npm run generate-tsp-only:rlc --filter=server

# Generate all Azure LRO specs
npm run generate-tsp-only:azure-modular --filter=lro

# Exact matching still works as before
npm run generate-tsp-only:rlc --filter=routes

Backward Compatibility

All existing functionality is preserved:

• Exact path matching continues to work exactly as before
• No breaking changes to existing scripts or workflows
• Empty results when no matches are found (same behavior as before)

Testing

Comprehensively tested across all test types:

• ✅ RLC tests (rlc tag)
• ✅ Azure RLC tests (azure-rlc tag)
• ✅ Modular tests (modular tag)
• ✅ Azure Modular tests (azure-modular tag)
• ✅ Edge cases (non-existent filters, exact matches, partial matches)

Fixes #3431.

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