perf: cache read-heavy db queries with streamlit

[Aspect022]

Which issue does this PR close?

• Closes Implement @st.cache_data for DB Read Operations #136

Rationale for this change

Read-heavy database query functions like get_all_mappings() and get_categories() executed a SQLite lookup directly on every UI re-render, leading to excessive I/O overhead and UI lag.

What changes are included in this PR?

• Streamlit Caching: Wrapped all repetitive read query functions in engine/db.py (e.g. get_mapping, get_all_mappings, get_categories, get_mapping_count, get_metadata) with @st.cache_data(ttl=3600).
• Cache Invalidation: Added an internal _clear_db_cache() helper to forcefully clear the st.cache_data object whenever mutation functions occur (like insert_mapping, update_mapping, migrate_from_json, or restore_database).

Are these changes tested?

Yes, existing pytest integration and database utility tests passed and correctly handled the added caching logic.

Are there any user-facing changes?

Noticeable improvements in overall application performance and responsiveness, due to minimizing database queries across component renders. No functional changes were made to endpoints or structures.

[github-actions]

Thanks for creating a PR for your Issue! ☺️

We'll review it as soon as possible.
In the meantime, please double-check the file changes and ensure that all commits are accurate.

If there are any unresolved review comments, feel free to resolve them. 🙌🏼

[SharanyaAchanta]

Hey, thanks for the PRs! I was caught up with other merges yesterday. Since today is the final day, I’m wrapping things up. I see some checks are failing now—if you can resolve them quickly, let me know. If not, no worries at all, thanks for your contribution!

[Aspect022]

@SharanyaAchantai have made the changes can youcheck it out!