weather: Add some heuristics to GetCurrent*

[FintasticMan]

This means that there is a higher likelihood that the returned event is the most up-to-date current event. It chooses the event with the lowest expiry, and between events with the same expiry, it chooses the one with the latest timestamp.

Alternative to #1878.

I'm not the best when it comes to working with references to unique_ptrs etc, so if there's a better way to keep track of the best option so far, I'd like to hear it.

[github-actions[bot]]

Build size and comparison to main:	Section	Size	Difference
text	376880B	80B
data	940B	0B
bss	63420B	0B

[FintasticMan]

Superseded by #1890.