Add a micros() variant for more precise timing control

[SunitRaut]

Add an optional micros() variant to add precision to timing control, allowing for higher frequency operations.
This should be added in a way such that it is easier for users to understand the difference between millis() and micros() variant and makes it easier for users to choose preferred variant.

One way to achieve this is to keep millis() as the default variant and let micros() be an additional variant.