Allow parallel_count=0 to skip query workers while still running checkpoint validation

When parallel_count is 0, no query workers are spawned and throughput
metric returns 0. Checkpoint validation continues to run from the ETL
pipeline loop using its own executor, unaffected by the absence of
query workers.

Author: phillipleblanc

crates/test-framework/src/spicetest/datasets/mod.rs

@@ -266,10 +266,6 @@ impl SpiceTest<NotStarted> {
             return Err(anyhow::anyhow!("Query set is empty"));
         }
 
-        if self.state.parallel_count == 0 {
-            return Err(anyhow::anyhow!("Parallel count must be greater than 0"));
-        }
-
         // Ensure executor is configured
         let executor = self
             .state
@@ -481,6 +477,9 @@ impl SpiceTest<Completed> {
     }
 
     pub fn get_throughput_metric(&self, scale: f64) -> Result<f64> {
+        if self.state.parallel_count == 0 {
+            return Ok(0.0);
+        }
         // metric = (Parallel Query Count * Test Suite Query Count * 3600) / Cs * Scale
         let lhs = self.state.parallel_count * self.state.query_count * 3600;
 

src/commands/load/mod.rs

@@ -1084,7 +1084,7 @@ pub(crate) async fn run(
                                     );
                                 }
                             }
-                        } else if !has_checkpoint_validation {
+                        } else if !has_checkpoint_validation && common_args.concurrency > 0 {
                             // When results validation is not enabled, wait for
                             // at least 1 query set iteration to complete so we
                             // collect meaningful query metrics before stopping.