v0.2.0-beta3

feat: cleanup timeout for process termination (#207)

Implement configurable cleanup timeout to control how long the system waits
for process cleanup verification before triggering forced shutdown. This
replaces the hardcoded 10-second timeout with a user-configurable value.

Configuration:
- Add --cleanup-timeout CLI flag (default: 10s, env: COG_CLEANUP_TIMEOUT)
- Flow: CLI → Config → Runner for proper field injection

Implementation changes:
- Replace hardcoded timeout with context.WithTimeout() pattern
- Improve check interval from 100ms to 10ms for more responsive detection
- Add injectable verifyFn field to Runner for comprehensive testing
- Update terminology from "ungraceful shutdown" to "forced shutdown"

Testing improvements:
- Migrate time-dependent tests to Go 1.25 synctest for deterministic execution
- Add comprehensive test coverage for timeout scenarios and multiple ForceKill calls
- Use safe high PID values (9999999) and proper mocking to prevent real process operations
- Configure linter to handle synctest patterns correctly

This enables users to customize cleanup wait times based on their specific
workload requirements while maintaining safe defaults.

* Address leaking coglets from test

The test harness now properly cleans up orphaned coglet processes when interrupted:

Key Features:
- Cross-platform compatibility: Works on both macOS (Darwin) and Linux
- Robust process discovery: Uses pgrep -f coglet as primary method, falls back to ps with platform-specific flags
- Safe process killing: Validates we can signal processes before attempting to kill them
- Process group cleanup: Kills both process groups and individual processes
- Safety measures: Never kills ourselves, our parent, or PID 1
- Signal handling: Responds to both SIGINT (ctrl+c) and SIGTERM

Implementation Details:
- killAllChildProcesses() finds and kills coglet processes during cleanup
- findCogletProcesses() tries pgrep first, falls back to ps
- Platform-specific ps flags: -ax on macOS, -e on Linux
- Process ownership validation through signal testing before killing
- Integrated into existing TestMain signal handler

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Co-Authored-By: Michael Dwan <m@dwan.io>
Co-authored-by: Morgan Fainberg <code@tempusfrang.it>