Add DateTime::with_time()

[pitdicker]

Reopening #1027.

We have now had three issues on how to create a DateTime for today at a specific time: #1022, #1447 and #1508.
We could add a today_at method to Local (and may still want to do so), but DateTime::with_time() is a more generic solution.

A second reason to want this method is it gives a way to deal with the one remaining panic case from #1047 that I don't have a workaround for: If users write dt.timezone().from_local_datetime(&dt.date().and_time(time)) it may panic when the NaiveDateTime in UTC is at the edge of the representable range, and the local NaiveDate is out of range. We can internally use overflowing_naive_local() and return a result if that is in range.

Renamed from set_time to with_time to match the other with_* methods.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.81%. Comparing base (920e73b) to head (221e640).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1510   +/-   ##
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  Coverage   91.80%   91.81%           
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  Files          40       40           
  Lines       18337    18351   +14     
=======================================
+ Hits        16835    16849   +14     
  Misses       1502     1502           

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