Add SPICE support for circuit-json simulation switches

[seveibar]

Summary

• generate voltage-controlled switch components and control sources for simulation_switch entries when converting to SPICE
• add unit and integration coverage for square-wave behavior driven by simulation switches
• bump the circuit-json dependency to the latest release

Testing

• bun test tests/unit/circuit-json-conversion.test.tsx
• bun test tests/integration/simulation.test.ts
• bunx tsc --noEmit

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https://chatgpt.com/codex/tasks/task_b_68e1aaee0188832ea9169969a9d6e68f

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid turning one-shot switches into periodic oscillators

In buildSimulationSwitchControlValue, the fallback branch constructs a PULSE source with period = closesAt * 2 whenever only closes_at is provided. That makes the control voltage toggle forever, because SPICE repeats the pulse each period seconds, and with TD = closesAt (often 0) the switch flips immediately instead of staying closed until the requested time. Simulation switches that are meant to close once and remain closed will instead chatter on and off, producing an incorrect circuit. Consider emitting a non-repeating waveform (e.g., a DC level with a single transition via PWL or a pulse with an extremely long period) and delaying the first transition so that starts_closed, closes_at, and opens_at are honored.

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