refactor(core): improve random_delays api

[cepetr]

This small PR slightly improves the API of the random_delays module by making the function names more consistent.

It reflects the fact that random_delays serves two purposes:

1. Provides a random generator for small delays that can be injected into any part of the code via the wait_random() function.
2. Implements Random Delay Interrupts (RDI).

The wait_random() function was not renamed to avoid introducing extensive changes, especially in legacy code, as this PR aims to be minimally intrusive.

This PR resolves #4197, although it addresses the problem in a different way.

[github-actions]

core UI changes	device test	click test	persistence test
T2T1 Model T	test(screens) main(screens)	test(screens) main(screens)	test(screens) main(screens)
T3B1 Safe 3	test(screens) main(screens)	test(screens) main(screens)	2724
T3T1	test(screens) main(screens)	test(screens) main(screens)	test(screens) main(screens)
All	main(screens)