test: salvage, migrate, and fix unused unit and integration tests

[sejubar]

Description

Revive/remove unused tests and clean up unit test excluding knowledge base tests

Fixes #issue_number

Type of change

(Please delete options that are not relevant)

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ⚡ New feature (non-breaking change which adds functionality)
• 📢 Breaking change (fix or feature that would cause existing functionality not to work as expected)
• 📄 This change requires a documentation update

Verification Process

To ensure the changes are working as expected:

• Test Location: Specify the URL or path for testing.
• Verification Steps: Outline the steps or queries needed to validate the change. Include any data, configurations, or actions required to reproduce or see the new functionality.

Additional Media:

• I have attached a brief loom video or screenshots showcasing the new functionality or change.

Checklist:

• My code follows the style guidelines(PEP 8) of MindsDB.
• I have appropriately commented on my code, especially in complex areas.
• Necessary documentation updates are either made or tracked in issues.
• Relevant unit and integration tests are updated or added.

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[ea-rus]

@ZoranPandovski, should be 'load' folder be kept? or moved to other repo if it has something useful?

[ea-rus]

it might be reworked in separated pr, it covers resp api tests
I will create an issue for it

[ea-rus]

maybe move all tests from ‎tests/unused/unit/handler_tests and tests/unused/unit/ml_handlers/ to handler folders? for example this one into mindsdb/integrations/handlers/apache_doris_handler/tests/
if we don't want to run them we can keep their code at least

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[sejubar]

signed and agreed to the CLA