feat(misc): return timezone aware datetime objects

[chgad]

let http_date_to_dt validate timezone information from the provided http-date and return timezone aware datetime objects remove tests for timezone naive variants amend tests

Breaks any application relying on naiveness of datetimes or interpretation in local time. Closes https://github.com/falconry/falcon/issues/2182

Summary of Changes

Make the function http_date_to_dt validate timezone inforamtion of a http-date and return timezone aware datetime objects.

Related Issues

2182

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (321bda1) to head (db6fe41). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2246 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 63 63 Lines 7329 7335 +6 Branches 1276 1277 +1 ========================================= + Hits 7329 7335 +6 ```

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