Allow to reset the INP calculation

Hi,

it would be awesome if the package would offer a `resetINP` function or something similar.

**Use case**
We would need this feature as we take a look at the "subpages" of SPAs as individual pages and would be highly interested in the individual INP values of them. Because of the way the entries are collected in `longestInteractionList` this of course is not really possible.

**Possible Solution**
I guess clearing `prevInteractionCount, prevInteractionCount, longestInteractionMap` in this new reset function should be enough? Or do I miss something here?

**Value**
This clear function would allow for more different use cases (in combination with the already present `reportAllChanges: true`) while increasing the complexity and package size only slightly. I think this is a valuable addition!
Thanks!

Start by tracing the INP calculation through longestInteractionList and the mentioned state variables prevInteractionCount and longestInteractionMap. Define what resetINP must clear for SPA subpage measurements, then verify that subsequent interactions produce independent INP values when reportAllChanges is enabled.

Written by the indexing model from the issue text.