Configure DuckDB memory limit based on available system RAM

[qodo-code-review]

Description

• DuckDB connections currently have no memory constraints, potentially causing out-of-memory issues
• System memory availability varies across deployment environments
• Need to dynamically calculate and apply appropriate memory limits at runtime

Deliverables

• RAM Calculation: Implement method to determine total system memory and current process memory usage
• Memory Limit: Set DuckDB connection pool memory limit to half of available RAM in GB
• Connection Pool: Update connection string to include calculated memory limit parameter

[linear]

DB-1770