[DOP-15561] Cast DateTimeHWM to DateTime64 in Clickhouse

[dolfinus]

Change Summary

DateTime precision in Clickhouse is only up to seconds. So using DateTimeHWM on column with higher precision, like DateTime64, can lead to reading the same value twice because fractional part of second is ignored.

Cast Python datetime type to DateTime64(6) in Clickhouse, keeping fractions of seconds. In case of using old Clickhouse versions (20.7 .. 21.0), users might have to update hwm.expression value, so this is a breaking change.

Related issue number

Checklist

• Commit message and PR title is comprehensive
• Keep the change as small as possible
• Unit and integration tests for the changes exist
• Tests pass on CI and coverage does not decrease
• Documentation reflects the changes where applicable
• docs/changelog/next_release/<pull request or issue id>.<change type>.rst file added describing change
  (see CONTRIBUTING.rst for details.)
• My PR is ready to review.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.34%. Comparing base (96ce940) to head (298c705).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #267   +/-   ##
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  Coverage    94.34%   94.34%           
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  Files          204      204           
  Lines         7963     7963           
  Branches      1408     1408           
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  Hits          7513     7513           
  Misses         325      325           
  Partials       125      125           

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