Require sustained coil current before relay switches

[esaruoho]

Summary

• Fixes relay incorrectly switching due to brief back-EMF transients (The relay component switches to the intermediate state immediately giving incorrect results for some circuits. #67)
• Adds threshold timers that require coil current to be sustained above/below the switching threshold for at least 50% of the switching time before the relay changes state
• Only affects the new relay model (switchingTime > 0); old model unchanged
• Threshold timers are cleared on reset

Test plan

• Place a relay with the new model (default) and verify normal switching works
• Verify brief current spikes (e.g., from back-EMF) don't trigger false switching
• Test with different switching time values
• Verify old model relays (switchingTime = 0) are unaffected
• Reset circuit → verify relay resets cleanly

Fixes #67

🤖 Generated with Claude Code

[esaruoho]

@pfalstad any takes on this?

[MatNieuw]

Why is a threshold timer needed? Because of the self-inductance of the coil, there is a noticeable delay before the current exceeds the "activate" threshold, I can see it both in real measurements measuring when the NC contact starts to open, and in simulation's scope. And does the back-EMF mentioned in #67 contain enough energy for the relay to start moving?