ci: run the embedded tests in simavr instead of Wokwi

[FredM67]

Summary

Wokwi CI uses paid credits, and they are nearly used up. simavr runs the same embedded tests for free: no limits, no account, no token, and it also runs locally (Linux/WSL).

The Wokwi setup only ever used a bare Arduino Uno (diagram.json has no parts and no connections). The tests only exercise the ATmega328P itself: CPU math, pin registers, UART and timers. simavr emulates all of that cycle-accurately.

Changes

• New uno_sim environment (platformio.ini). The tests run in simavr (platformio/tool-simavr, ATmega328P at 16 MHz, UART0 on stdout), and PlatformIO reads the Unity results itself. There is no upload step. Run it locally with pio test -e uno_sim.
• The tests now stop at the end. Each suite called UNITY_END() inside loop(), so it repeated forever or spun silently. Wokwi hid this by stopping at the first OK. A small helper, haltAfterTests() (test/embedded/halt_after_tests.h), is now called right after UNITY_END(): the suite runs once, and simavr exits (it quits when the CPU sleeps with interrupts disabled).
• CI: one "Embedded tests (simavr)" job runs every embedded test, benchmarks included. simavr counts cycles exactly, so their figures are reproducible. The job has a 15-minute timeout, so a hanging test fails instead of holding the runner for 6 hours.
• Removed from CI: the test discovery job, the Wokwi CLI install, the JUnit conversion, the test reporter, the checks: write permission and the use of WOKWI_CLI_TOKEN.
• Kept: wokwi.toml and diagram.json, so the tests can still be run interactively in the Wokwi VS Code extension.
• Docs: test/README.md and one outdated comment in test_voltage_accumulation.

Testing

• Locally in WSL: all 8 embedded tests pass under simavr (the 6 tests CI used to run plus the 2 _perf benchmarks), 93 test cases in ~1 min 40 s.
• Failures are detected: with a deliberately broken assertion, PlatformIO reports test_divu2: Expected 7 Was 1 [FAILED] and exits with code 1.
• actionlint passes.
• git merge-tree shows no conflicts with feat: support several remote load units #160, feat: decide the loads just before L1's zero crossing, on a predicted bucket #162 or perf: integer energy bucket, no float or division in the ADC ISR #163. The @date line of test_mult_asm is set to perf: integer energy bucket, no float or division in the ADC ISR #163's value so both branches make the same change.

Notes

• The pre-commit hooks also cleaned up existing trailing whitespace and a missing final newline in test_mult_asm and test_voltage_accumulation.
• Once this is merged, the WOKWI_CLI_TOKEN secrets (Actions and Dependabot) are no longer used and can be deleted.

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