[HUDI-7704] Unify test client storage classes with duplicate code

[wombatu-kun]

Change Logs

TestHoodieClientOnCopyOnWriteStorage and TestHoodieJavaClientOnCopyOnWriteStorage have a bunch of duplicate code, so i:

• extracted common code (with some parameterizations) to HoodieWriterClientTestHarness class;
• removed unused code;
• moved static assertions-methods to existing separate class Assertions.

I did not add, remove or change subject of any test, I've just refactored these classes to avoid code duplications.

Impact

none

Risk level (write none, low medium or high below)

none

Documentation Update

none

• The config description must be updated if new configs are added or the default value of the configs are changed
• Any new feature or user-facing change requires updating the Hudi website. Please create a Jira ticket, attach the
  ticket number here and follow the instruction to make
  changes to the website.

Contributor's checklist

• Read through contributor's guide
• Change Logs and Impact were stated clearly
• Adequate tests were added if applicable
• CI passed

[danny0405]

cc @the-other-tim-brown for the code reviewing.

[hudi-bot]

CI report:

• c468c73 Azure: SUCCESS

Bot commands

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