Fix forecast query key bug

[kevinherdez]

• Overnight Caching is different than some users expect #1154

We do not correctly calculate the nominalDate that we attach to the query key for the useAvalancheForecast call. The issue was that we were incorrectly assuming that the expires_time field returned in the avalanche center metadata was an integer. However, there are at least 3 centers that return a float to specify that the forecasts expired on the half hour. For example, NWAC's expires time is 18.5.

We were creating a timestamp using the time passed in as the hour so the expires time for 18.5 was 18.5:00:00 instead of 18:30:00. The invalid time was being changed to 00:00:00 and leading to an incorrect nominal date because requestedTime was guaranteed to be before expiresTime.

I created a helper function that correctly creates the string and added tests