Adds the runtime plumbing that Phase 1b's SPICE event loop will drive:
- `publishVoltage(componentId, pin, voltage)` updates a (componentId,
pin) → volts cache and notifies every matching subscriber.
- `getCurrentVoltage(...)` reads the cache (was previously stubbed
null).
- subscribe/publish routing exercised by 7 new unit tests.
The scheduler still does not yet drive ngspice — `start()`,
`onMcuPinChange()` are unchanged. But once Phase 1b's solve loop is in
place, calling `publishVoltage` after each `readVec` is all the wiring
needed for components to start reacting to SPICE-resolved analog
states. This is the smallest non-trivial step that keeps the
architecture honest (no test-only emitters; the same code path will be
used in production).
Tests skip booting the WASM worker — they call publishVoltage
directly, so they pass in plain Vitest with no JSDOM Worker shim.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
davidmonterocrespo24