js-vextensions

* Fixed that Bridge class, with channel_safeCallbacks enabled, would generate callback-ids that were fractions (this causes problems in some cases, when the JSON structure gets decoded by another language/platform, with lower/different floating-point fractional-portion handling, as is true for rust/serde_json apparently); now switching to a random integer between 0 and MAX_SAFE_INTEGER. (which *should* work, at least with rust/serde_json as the middleman)

* Fixed that Timer's callback function could get called twice, if TimerContext.ManuallyTriggerOverdueTimers() was called (just before a timer.Start(0) timeout resolved).

* Made the logic within Timer.Start a more intuitive/robust. (from what I can tell)

* Added defensive call to ClearIntervalOrTimeout() just before each of the two Timer class' code-lines that starts a new interval/timeout.