Color/MonoCamera `frameEvent` output, per-frame IR control

[alex-luxonis]

ColorCamera/MonoCamera: add frameEvent output, to be used for IR control, etc.

• Outputs metadata-only ImgFrame message as an early indicator of an incoming frame. Fields populated for now: camera id, sequence number, timestamp
• It's sent on the MIPI SoF (start-of-frame) event, just after the exposure of the current frame has finished and before the exposure for the next frame starts.
• Could be used to synchronize various processes associated with per-frame control of camera capture: IR dot/flood alternate, manual exposure/focus, etc. Especially with a Script node running on device for low latency control

Add new Script API, similar in functionality to the respective host API:

• Clock.now() -> datetime.timedelta
  • at the moment this returns a timestamp based on the device monotonic clock, not synced to host time
• Device.setIrLaserDotProjectorBrightness(mA: float) -> bool
• Device.setIrFloodLightBrightness(mA: float) -> bool
• Device.getIrDrivers() -> List[Tuple[str, int, int]]

TODO: add C++ example to illustrate the usage

Misc:

• Script: add optional name parameter to setScriptPath, might come handy if the path is long, to have a shorter identifier

[Luxonis-Brandon]

This is SWEET!

[themarpe]

@alex-luxonis Would it be better to integrate this (IR switching) directly into the Color/MonoCamera node to provide for an easier use and expose a property to enable? (the node would then check if IR driver is available, and take as much control over it as it needs to)?

[themarpe]

@alex-luxonis thoughts on making this a native node instead? And or integrating directly into Color/MonoCamera?

CC: @moratom on impl. afterwards

[alex-luxonis]

Yes, later we should simplify the usage. frameEvent would be still useful though for custom things, e.g. by toggling a GPIO controlling an external strobe light.