Function execute_subplan 

pub async fn execute_subplan(
    plan: &LogicalPlan,
    params: &HashMap<String, Value>,
    outer_values: &HashMap<String, Value>,
    graph_ctx: &Arc<GraphExecutionContext>,
    session_ctx: &Arc<RwLock<SessionContext>>,
    storage: &Arc<StorageManager>,
    schema_info: &Arc<Schema>,
    mutation_ctx: Option<&Arc<MutationContext>>,
) -> Result<Vec<RecordBatch>>

Execute a logical plan using a fresh HybridPhysicalPlanner with the given params.

Shared by RecursiveCTEExec, GraphApplyExec, and ExistsExecExpr. Pass mutation_ctx = Some(...) to enable writes inside the sub-plan (CALL { ... SET/CREATE/MERGE/DELETE }). None is appropriate for read-only sub-plans (Locy rule evaluation, EXISTS predicate).