feat(sim): simulate relay diversion

[FredM67]

Summary

grid_sim now simulates relay diversion, with three scenarios run against a firmware with two relays.

grid_sim

• relay <pin> <phase> <W>: a resistive load on a relay - it follows its pin at once, with no zero-crossing latching.
• Per load, the shortest complete ON and OFF periods; the summary shows them for relays:

  Relay D8    L1  1500 W:    2 switch-ons, on  44.1 %,   80.83 Wh, first on at 126.001 s
            shortest ON 120.0 s, shortest OFF 120.0 s (complete periods; -1: none)
  

• New expectations: expect switches <pin> <min> <max>, expect min_on <pin> <s>, expect min_off <pin> <s>.

Firmware: configs/relays.patch

Two relays on D8 and D9: in at 1000 / 2000 W of export, out above 200 W of import, 2 minutes minimum ON and OFF, a 1-minute filter. Built in .pio/build-relays (PLATFORMIO_BUILD_DIR), so the basic firmware of make check stays.

The minimum times are longer than the 1-minute settle time the relay engine waits after any change. With 1-minute minimums, the settle time alone produced the very same holds, and a firmware ignoring the minimum times passed relay_min_times. Checked: such a mutant now fails both relay_steps and relay_min_times (it lets go after 91 s instead of 120 s).

Scenarios (make check-relays)

Scenario	Checks
relay_steps	relays come in by threshold, each once, not before their minimum OFF time from power-up; with import they go out in reverse order, a settle time apart
relay_min_times	relay 1 held ON through an import, then OFF through a returning surplus, for its minimum times
relay_import_first	import is cut first: relay 1 goes out before relay 2 while relay 2 is within its minimum ON time (intended - minimising import comes before the relays' order)

24 expectations; the three scenarios take ~80 s in parallel. They run in a CI job of their own, "Grid simulation (relays)", alongside the existing one, which does not get longer.

Test plan

• the three relay scenarios pass: 10/10, 7/7, 7/7
• a firmware without minimum ON/OFF times fails relay_steps and relay_min_times
• make check unchanged (30/30)
• actionlint, pre-commit

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