Streamline local test environment setup

[schlessera]

Refactored the test environment setup to make it more robust and user-friendly. This consolidates multiple test commands and improves process management for local development.

Fixes #819

What Changed

• Added shell scripts to manage test environment lifecycle
• Consolidated PHPUnit commands to auto-detect version and config
• Improved process management with proper PID tracking
• Added mitmproxy version verification (≥11.0.2 required)
• Adapted CONTRIBUTING.md to explain the new setup

The main improvement is the simplified test workflow. Instead of juggling different commands for PHPUnit versions and remembering to start/stop test servers, everything is now handled through clear, single-purpose commands.

New Scripts

• scripts/start-test-environment.sh - Boots test and proxy servers - should be sourced to set environment vairables
• scripts/stop-test-environment.sh - Clean shutdown of all processes
• scripts/run-phpunit.sh - Version-agnostic PHPUnit runner

Usage

Basic testing is now simpler:

composer test # Run tests (auto-detects PHPUnit version)
composer coverage # Same, but with coverage

For development with local test servers:

# Direct usage (sets env vars in your shell)
source scripts/start-test-environment.sh
scripts/run-phpunit.sh
scripts/stop-test-environment.sh

# Or through composer (automated start/stop)
composer test:withserver
composer coverage:withserver

[jrfnl]

Future scope: add a Docker config file to get up & running with even less effort (and which would work on Windows too).

[jrfnl]

Just noticed, just running the script on my machine created some .test-pids/*.pid files. You may want to add those to the .gitignore file ?

[schlessera]

I changed the folder where PIDs are stored and added that location to .gitignore: tests/utils/pids

[jrfnl]

Just checking - this PR relates to #819 (and closes it ?)