experimental: add a converter for logical plan to sql

[ChunxuTang]

After we have the logical plan built, besides creating a native physical execution plan for data fusion and lanceDB, there's another option to convert the logical plan to SQL. It would allow us to implement some SQL optimizations, as well as leverage lanceDB vector search features.

Currently, the SQL converter supports:

• ScanByLabel - Node scanning with properties
• Filter - WHERE clause conditions
• Project - SELECT projections
• Distinct - DISTINCT modifier
• Limit - LIMIT clause
• Offset - SKIP/OFFSET clause

Doesn't support:

• Expand - Relationship traversal
• VariableLengthExpand - Variable-length paths
• Join - Complex joins
• Sort - ORDER BY clauses