Refactor and improve database migration code patterns

[coderabbitai]

Context

As discussed in PR #6286 (#6286), the current migration code for v0.31.0 follows patterns inherited from previous migrations (e.g., v0.26.0). While this approach works, there are opportunities to improve the migration code quality and consistency across all migration files.

Objectives

• Review and refactor migration code patterns across all existing migration files
• Improve error handling, logging, and progress reporting in migrations
• Ensure consistency in code style and structure across migration modules
• Update helper functions and utilities used in migrations
• Add or improve documentation for migration patterns

Scope

This is a follow-up to PR #6286 which focused on removing the Indices column and providing a working migration path. The improvements should be addressed systematically across all migration files in src/db/migration/.

References

• Original PR: fix: remove unique events logic from the ChainGetEvents API #6286
• Comment thread: fix: remove unique events logic from the ChainGetEvents API #6286
• Requestor: @akaladarshi

Notes

This work was deferred from PR #6286 to keep that PR focused on its core functionality (removing Indices column and adding migration logic) and to allow for a more thorough, systematic improvement of all migration code in a dedicated PR.