Add documentation for --static-analysis-tool=phpstan CLI option

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This PR adds comprehensive documentation for the --static-analysis-tool=phpstan CLI option that was introduced in #2098.

Changes Made

1. Added Missing CLI Option Documentation

Added documentation for the --static-analysis-tool option in src/guide/command-line-options.md that was previously missing. The documentation includes:

• Clear explanation of what static analysis integration does
• Usage examples with PHPStan
• Step-by-step workflow description
• Requirements and setup instructions
• Performance benefits and optimization details

2. Enhanced Configuration Documentation

Updated src/guide/usage.md with:

• Improved description of the staticAnalysisTool configuration option
• New dedicated "Static Analysis Integration" section explaining the feature in detail
• Comprehensive guide on why and how to use static analysis with mutation testing
• PHPStan setup and configuration instructions
• Example workflows and command usage

Key Features Documented

The documentation explains how static analysis integration:

• Catches escaped mutants that test suites might miss
• Identifies type violations, dead code, and unreachable code paths
• Runs only on escaped mutants for optimal performance
• Integrates seamlessly with existing Infection workflows

Example usage:

# Enable PHPStan integration
infection --static-analysis-tool=phpstan

# With additional options
infection --static-analysis-tool=phpstan --static-analysis-tool-options="--memory-limit=1G"

This addresses the documentation gap for a significant new feature that enhances mutation testing effectiveness by combining it with static analysis.

Fixes #281.

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