Add register_hwm_type to old_hwm classes

[maxim-lixakov]

Change Summary

• Add @register_hwm_type decorator to old_hwm classes to keep compatibility with use of hwm_type from onetl library
• update tests

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

Merging #46 (00b096d) into develop (ab64f8e) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop      #46      +/-   ##
===========================================
+ Coverage    95.40%   95.43%   +0.03%     
===========================================
  Files           48       48              
  Lines         1045     1052       +7     
  Branches       174      178       +4     
===========================================
+ Hits           997     1004       +7     
  Misses          27       27              
  Partials        21       21              

Files	Coverage Δ
etl_entities/old_hwm/date_hwm.py	100.00% <100.00%> (ø)
etl_entities/old_hwm/datetime_hwm.py	100.00% <100.00%> (ø)
etl_entities/old_hwm/file_list_hwm.py	97.18% <100.00%> (+0.08%)	⬆️
etl_entities/old_hwm/hwm.py	100.00% <100.00%> (ø)
etl_entities/old_hwm/int_hwm.py	100.00% <100.00%> (ø)