test: Add edge case tests for tool result conversion and Redis filter expressions

[alxkm]

Adds comprehensive edge case testing across two components:
Tool Call Result Converter:

• Empty collections (List, Map, arrays) → proper JSON empty structures
• Java records → correct JSON serialization
• Special characters in strings → proper JSON escaping (", \n, \t, )

Redis Vector Store Filter Expressions:

• Special Redis characters (@, {, }, |) → proper escaping
• Empty string values → correct Redis syntax ({})
• Single-item IN expressions → optimized formatting
• Field names with whitespace/quotes → proper quoting

Improves test coverage for collections containing special characters and empty collections.