Fix various docstring issues across multiple classes

[seladb]

Description

This PR corrects and improves docstrings in several classes:

• Removes redundant docstrings from __init__ methods in ConnectionHandler and TortoiseContext
• Fixes parameter name typo in Aggregate class docstring (is_distinct → distinct)
• Adds missing db_default parameter documentation to Field class
• Improves docstrings in Like and Index classes with proper parameter documentation

Motivation and Context

These fixes improve the accuracy and consistency of the API documentation.

How Has This Been Tested?

This is a documentation-only change with no functional code changes. The changes were verified by:

• Running linting/type checking to ensure no regressions
• Checking that docstrings are properly formatted

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.