PerfDiff: Fix documentation and formatting issues

[coderabbitai]

Description

Documentation and formatting issues that affect code readability and maintenance.

Issues Identified from PR #565

Markdown Formatting Issues

• docs/ci-performance.md:41: Multiple consecutive blank lines (Expected: 1; Actual: 2)
• LanguageTool grammar warnings about spacing throughout the document

Missing Documentation

• Several new classes and methods lack comprehensive XML documentation
• Public and internal APIs need clear, practical explanations per coding guidelines

Formatting Standards

• Various spacing and formatting issues identified by automated tools
• Inconsistent code formatting across new PerfDiff files

Affected Files

• docs/ci-performance.md
• Multiple files in src/tools/PerfDiff/ directory
• New DataContract classes
• Regression strategy implementations

Suggested Solutions

• Fix markdown formatting issues (remove extra blank lines)
• Add comprehensive XML documentation for all public/internal APIs
• Run dotnet format on all modified files
• Address LanguageTool grammar suggestions in documentation

Reference

• Original PR: feat: modularize PerfDiff regression detection, update analyzer reporting, and clarify CI performance documentation #565
• markdownlint-cli2, LanguageTool, and GitHub Check reports