Add from_timestamp_secs method to DateTime

[jasonaowen]

Add a new single-argument function for creating a DateTime from a Unix timestamp, to match from_timestamp_micros, from_timestamp_millis, and from_timestamp_nanos.

Resolves #1716 Suggestion: add DateTime::from_timestamp_secs function

[codecov]

Codecov Report

❌ Patch coverage is 95.91837% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.79%. Comparing base (59d5f46) to head (fd92d74).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/datetime/serde.rs	75.00%	1 Missing ⚠️
src/naive/datetime/serde.rs	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1719      +/-   ##
==========================================
+ Coverage   90.78%   90.79%   +0.01%     
==========================================
  Files          39       39              
  Lines       16231    16254      +23     
==========================================
+ Hits        14735    14758      +23     
  Misses       1496     1496              

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[djc]

Thanks!

[jasonaowen]

I slimmed down the tests, refactored the existing code to use from_timestamp_secs and from_timestamp_millis, and rebased onto main. I think this is ready to re-review!

[djc]

I slimmed down the tests, refactored the existing code to use from_timestamp_secs and from_timestamp_millis, and rebased onto main. I think this is ready to re-review!

Please squash your commits into a single one.

[jasonaowen]

Relocated and squashed!

[djc]

Thanks!