Add query expansion feature for neuroscience search

[zohaib-7035]

Summary:
This PR introduces a query expansion feature in the ks_search_tool.py module to improve search results for neuroscience-related terms. It automatically expands user queries with relevant synonyms or related concepts before performing searches.

Changes made:

1. Added a QUERY_SYNONYMS dictionary containing neuroscience keywords and their synonyms.

2. Implemented the expand_query() function:

   • Expands full phrases first, then individual words.
   • Prevents duplicate terms in expanded queries.

3. Integrated query expansion in the smart_knowledge_search() function so that all searches now automatically use expanded queries.

4. Added test code at the end of ks_search_tool.py to demonstrate query expansion.

Benefits:

• Increases search coverage and recall for domain-specific terms (e.g., "mouse brain" now searches for "Rattus norvegicus" and "somatosensory cortex").
• Reduces the chances of missing relevant datasets due to synonym mismatches.
• Fully backward compatible — if no expansion is needed, the original query is used.

Example:

• Input query: mouse brain
• Expanded query: mouse brain Rattus norvegicus somatosensory cortex
• Input query: memory
• Expanded query: memory hippocampus

Next steps / Future improvements:

• Expand the QUERY_SYNONYMS dictionary with more neuroscience terms.
• Consider loading synonyms from a JSON file for easier maintenance.
• Integrate with async search to handle large batch queries more efficiently.