refactor: update get_table_schema and enforce allowed_tables

[srikanth-karthi]

Summary

This pull request introduces two main changes:

• Adds a --allowed_tables CLI argument to restrict which tables can be queried in read-only mode.
• Simplifies the get_table_schema function by removing the database_name parameter. It now uses the database name from the connection directly.

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Changes

• Introduced --allowed_tables CLI argument for whitelisting tables.
• Enforced allowed_tables inside run_query to reject unauthorized table access.
• Removed the database_name argument from get_table_schema.
• Updated the get_table_schema implementation to use DBConnectionSingleton for the database name.
• Updated test cases and added new ones for the allowed table logic and modified schema function.

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Testing

• ✅ Verified that queries to non-whitelisted tables are blocked with a proper error message.
• ✅ Validated that get_table_schema works correctly without the database_name argument.
• ✅ Ensured all previous tests continue to pass.
• ✅ Performed manual tests using the MCP CLI.

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User Experience Improvements

Feature	Before	After
Allowed table restriction	Not available	Available via --allowed_tables CLI argument
Schema fetching (get_table_schema)	Required explicit database_name	Automatically uses the configured connection’s DB

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Breaking Change

❌ No. This change is backward compatible.

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RFC / Issue

Not applicable.

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Checklist

• Reviewed contributing guidelines
• Self-reviewed the changes
• Verified tests pass
• Documentation updated
• Feature tested manually

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Acknowledgment

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of the project license.