Documentation should use more specific types

Currently, the documention uses types like "unsigned long" (for example here: https://www.arduino.cc/en/Reference/millis). However, this is only correct for the AVR architecture, on e.g. the Due a long is (AFAIK) 64 bit, but the code explicity uses `uint32_t`. It would make sense to adopt the same explicit approach in the documentation (and, while we're at it, probably apply this to the code of the AVR port as well).

Start with the millis reference page linked in the issue, then inspect the AVR port where the implementation already uses uint32_t and compare the documentation's type wording across architectures. Done means the affected documentation uses architecture-appropriate explicit types, with the AVR port addressed if that scope is confirmed.

Written by the indexing model from the issue text.