Fixes and improvements to powerMonitor

[SRWieZ]

See NativePHP/electron#143

• src/Client/Client.php: PowerMonitor passes parameters to one of its endpoints. Unfortunately, they were not sent by the client.
• PowerMonitor::class now implements Contracts\PowerMonitor::class interface
• Facades\PowerMonitor::fake() swaps implementations with a test double concrete
• Implement PowerMonitorFake::class with assertion helpers
• Test that PowerMonitorFake::class assertions work

I plan to submit another PR with a fix for phpstan.neon, which is currently not working, and add a GitHub action to check every push.

[SRWieZ]

Ready for review!