Reduce scheduler fiber stack size for tests

Use the new fiber stack size option to reduce the amount of stack size allocated for each fiber.

The tests do not need a whole meg's worth of stack per fiber, and some of the 32-bit tests can exceed the amount of free memory avaliable.

src/marl_test.h

@@ -57,6 +57,7 @@ class WithBoundScheduler : public testing::TestWithParam<SchedulerParams> {
     marl::Scheduler::Config cfg;
     cfg.setAllocator(allocator);
     cfg.setWorkerThreadCount(params.numWorkerThreads);
+    cfg.setFiberStackSize(0x10000);
 
     auto scheduler = new marl::Scheduler(cfg);
     scheduler->bind();