fix type and nil panic errors

1. Added Err() method to CollectedResult (pkg/neo4j/neo4j.go:68-72):
    - The resultiter.Neo4jResultIterator interface requires Err() error
    - CollectedResult was missing this method, causing the type assertion to fail
    - Since CollectedResult pre-fetches all records, Err() always returns nil
  2. Fixed nil pointer dereference in buildCypherQuery (pkg/neo4j/query-events.go:173):
    - Changed if *f.Limit > 0 to if f.Limit != nil && *f.Limit > 0
    - This prevents a panic when filters don't specify a limit
  3. Simplified parseEventsFromResult signature (pkg/neo4j/query-events.go:185):
    - Changed from func (n *N) parseEventsFromResult(result any) to accept *CollectedResult directly
    - This eliminates the runtime type assertion since ExecuteRead already returns *CollectedResult
    - Removed the now-unused resultiter import

pkg/neo4j/neo4j.go

@@ -65,6 +65,12 @@ func (r *CollectedResult) Len() int {
 	return len(r.records)
 }
 
+// Err returns any error from iteration (always nil for pre-collected results)
+// This method satisfies the resultiter.Neo4jResultIterator interface
+func (r *CollectedResult) Err() error {
+	return nil
+}
+
 // init registers the neo4j database factory
 func init() {
 	database.RegisterNeo4jFactory(func(