Use UTC times consistently

Regarding this comment:
https://github.com/rstudio/pins-python/blob/d215a8cd6cf958be0f4fc41c6e90e21c907b4655/pins/versions.py#L77-L78

As far as I can tell, R pins will write the created datetime as a UTC time:

https://github.com/rstudio/pins-r/blob/de47c3141d97020e9f4a6a2e93d5823bc649105b/R/meta.R#L50

And the functions it uses to parse datetimes also specify UTC (although the two parse_ functions indeed strip it out).
https://github.com/rstudio/pins-r/blob/de47c3141d97020e9f4a6a2e93d5823bc649105b/R/meta.R#L55-L68

I haven't looked into this too deeply though.

As far as I can tell, Python pins will just use the local datetime, e.g.
https://github.com/rstudio/pins-python/blob/d215a8cd6cf958be0f4fc41c6e90e21c907b4655/pins/versions.py#L104

I suggest that this behaviour is changed (this is arguably a breaking change, arguably a bugfix) to use UTC consistently everywhere. To that end, the DTZ rules in ruff could be helpful to enable.

In any case, I think it would be worth documenting this behaviour in more detail.

Start by reading pins/versions.py around lines 77-78 and 104, then compare its datetime handling with the linked pins-r implementation. Check where Python pins writes and parses created timestamps, and document the resulting UTC behavior; completion should cover the relevant paths consistently and address the suggested Ruff DTZ rules.