Add Delay implementation for qingke v4

[romainreignier]

I have made a draft PR on ch32-hal-template ch32-rs/ch32-hal-template#1 to add the option to not use embassy on the generated template but we would need a Delay implementation for qingke v4.

One could use this:

qingke::riscv::asm::delay(10_000_000);

for a template for beginners, I find that a real delay in milliseconds is easier to use.

[andelf]

Agreed.
A delay implementation is necessary when embassy is not enabled.

WCH's MCU is slow when running on FLASH. So the delay might be incorrect due to flash latency.