fix(threadpool): batches run every task once, and Stop ends the whole pool

- Enqueue(vector) dropped tasks when the count didn't divide by the
  workers: the last one got only the remainder. Tasks are now split as
  evenly as the count allows, each worker's taskCount grows by what it
  was given (the single-task Enqueue picks by it), and Start(1), which
  has no workers, leaves the batch for the caller's JoinPool.
- Stop wakes every slot, JoinPool's too, after joining the workers: a
  thread that had joined the pool slept on. It takes each slot's mutex
  before notifying, so a waiter between its check and its sleep can't miss
  the wake-up, and works on the pool it started with. Again, or before
  Start, it does nothing; joining a thread twice threw. Its documentation
  says what it doesn't do: stop from a pool task, or from two threads at
  once, run tasks enqueued once it has begun, or have JoinPool wait for it.
- Tests: EnqueueBatch, StopJoinPool.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

project.cpp

@@ -23,5 +23,11 @@ extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> a
     };
     cfg.GetInterfacesAndImplementations(ifaces, impls);
 
+    // Tests link this project's static library; wasm builds run no tests.
+    if (cfg.target.find("wasm") == std::string::npos) {
+        cfg.AddTest("EnqueueBatch").Dependencies({ &cfg });
+        cfg.AddTest("StopJoinPool").Dependencies({ &cfg });
+    }
+
     return cfg;
 }