Summary

As noted in discussion on#18263, theid parameter is optional on ports that support virtual timers.

Explain this in the docs, and add some more general explanation of hardware vs virtual timers.

This work was funded through GitHub Sponsors.

Testing

Manually checked the ports for which are hardware-only and which are virtual-only:

• Hardware-only is cc3200, nrf, renesas-ra, stm32, and esp32 pendingesp32/machine_timer.*: Adding support for Timer(-1) soft/virtual timers. #18263.
• Virtual-only is rp2 and Zephyr.

Explained this in the docs by saying hardware timers are generally available, apart from the two exceptions, and that virtual timers are only available on some ports.