Fix Cypher syntax error in relationship operations

[mlesyk]

Summary

Fixes #44
Fixes bug preventing relationship creation/deletion due to invalid Cypher syntax.
See neo4j Cypher syntax docs

Problem

The create_relations and delete_relations methods used invalid Cypher syntax $(relation.relationType) which caused Neo.ClientError.Statement.SyntaxError.

Error: {code: Neo.ClientError.Statement.SyntaxError} {message: Invalid input '$': expected a node label/relationship type name, '%' or '(' (line 6, column 29 (offset: 204))
"            MERGE (from)-[r:$(relation.relationType)]->(to)"
                             ^}					 

First problem - syntax error

MERGE (from)-[r:$(relation.relationType)]->(to)

Second - two times iteration over relations

for relation in relations:
...
            self.neo4j_driver.execute_query(
                query, 
                {"relations": [relation.model_dump() for relation in relations]}

Changes

• ✅ create_relations(): Fixed syntax + added batch processing
• ✅ delete_relations(): Fixed syntax + added batch processing
• ✅ Added regex validation for relationship types

Testing

• ✅ Creation and deletion workflow tests passed, they were failing before fix (mcp-neo4j-memory\tests\test_neo4j_memory_integration.py)
• ✅ Single and batch operations tests using Claude Desktop
• ✅ Input validation edge cases tests using Claude Desktop