Provide Context object to avoid RTC calling SystemTime::now().

[jamesyoungman]

The RTC should not call SystemTime::now() because the RTC is part of the V memory implementation, and that needs to be able to run in environments (e.g. WASM) that lack support for SystemTime::now().

(In a WASM environment, SystemTime::now() will panic)

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Tested manually by running hello.tape.