Give API to get non-buggy time (millis_64())

[Ten0]

Describe your core improvement

I’m trying to obtain the current timestamp at a specific time t1, and check for its validity later at t2 by making sure t2-t1<max_delay.

I know of millis(), but I want a more reasonable version that won’t do crazy things like wraparound on the int32 and consider my things “recent” after 49.7 days because of the overflow.

Something like in the scheduler, using an int64: Blaming esphome/esphome/core/scheduler.cpp at d3592c451bc8570419126c8d753ec05ff5c8d55e · esphome/esphome · GitHub

Current limitations

Currently that method of the scheduler is private, so I can’t access it via App.scheduler.millis_64_(millis()).
That sounds reasonable because it was recently modified, but ESPHome probably deserves some public way to access some form of i64 now
(e.g. App.now() or something along those lines).

Technical benefits

Easily get a reasonable millis() that won't cause wraparound bugs.

[Ten0]

https://community.home-assistant.io/t/how-to-get-current-non-buggy-time-millis-64/930391/2?u=ten