fix(mypy): Resolves regression introducted in #9824

[john-bodley]

SUMMARY

This PR fixes a regression introduced in #9824 and additional makes from_dttm/to_dttm optional (unrelated to the regression PR).

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TEST PLAN

CI and confirmed the change locally.

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

to: @serenajiang

[codecov-commenter]

Codecov Report

Merging #9973 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #9973   +/-   ##
=======================================
  Coverage   71.35%   71.36%           
=======================================
  Files         585      585           
  Lines       30917    30917           
  Branches     3246     3246           
=======================================
+ Hits        22061    22064    +3     
+ Misses       8747     8744    -3     
  Partials      109      109           

Flag	Coverage Δ
#cypress	54.00% <ø> (-0.08%)	⬇️
#javascript	59.39% <ø> (ø)
#python	71.54% <100.00%> (+0.03%)	⬆️

Impacted Files	Coverage Δ
superset/connectors/sqla/models.py	90.51% <ø> (ø)
superset/common/query_object.py	89.42% <100.00%> (ø)
superset/tasks/cache.py	73.91% <100.00%> (ø)
superset/utils/core.py	89.18% <100.00%> (ø)
...rontend/src/SqlLab/components/QueryAutoRefresh.jsx	65.90% <0.00%> (-6.82%)	⬇️
superset/sql_lab.py	78.26% <0.00%> (+0.43%)	⬆️
superset/result_set.py	98.31% <0.00%> (+1.68%)	⬆️
superset/db_engine_specs/sqlite.py	73.33% <0.00%> (+10.00%)	⬆️

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