feat: show filtered clone count in reports and improve test coverage

[ericodx]

Summary

• Show how many clones were filtered by configuration (ignoreSameFile, ignoreStructural) in TextReporter and HtmlReporter, so users understand why "No clones detected" appears when filters are active
• Fix integration test that depended on project's .swift-cpd.yml config file
• Improve test coverage for UnifiedTokenMapper, CTokenizerScanner, and BehaviorSignatureExtractor

Type of Change

• feat: A new feature has been added.
• fix: A bug has been fixed.
• test: Addition or correction of tests.
• docs: Changes only to the documentation.
• ci: Changes related to continuous integration and deployment scripts.
• build: Changes that affect the build system or external dependencies.
• chore: Other changes that do not fit into the previous categories.
• revert: Reverts a previous commit.
• perf: A code change that improves performance.
• refactor: A code change that neither fixes a bug nor adds a feature.

Invariants Checklist

• Detection is deterministic (same input → same output)
• Source files are never modified (tool is read-only)
• Source locations are accurate (file, line, column)
• No false negatives introduced (previously detected clones are still detected)
• Performance not degraded for large codebases
• Swift 6 Strict Concurrency compatible
• Pipeline stages remain stateless pure transformations

Pipeline Impact

Which stages are affected?

• FileDiscovery
• Tokenization
• Normalization
• Detection (Type 1 / Type 2 / Type 3 / Type 4)
• Reporting
• CLI / Configuration
• Cache / Baseline
• None

Testing

• Unit tests added or updated
• Tests use TokenFactory / TempFileHelper / AnalysisHelper where appropriate
• Integration tests added or updated (if detection or pipeline logic changed)
• Both positive cases (expected clones) and negative cases (false positives to avoid) covered
• All tests pass locally (swift test)