- Temp allocator now supports more than 2 in-flight stacks.

- Printing stacktrace uses its own temp allocator.
- `@pool` no longer takes an argument.
- `Allocator` interface removes `mark` and `reset`.
- DynamicArenaAllocator has changed init function.
- Added `BackedArenaAllocator` which is allocated to a fixed size, then allocates on the backing allocator and supports mark/reset.

lib/std/core/runtime_test.c3

@@ -244,7 +244,7 @@ fn bool run_tests(String[] args, TestUnit[] tests) @private
 	name.append_repeat('-', len - len / 2);
 	if (!context.is_quiet_mode) io::printn(name);
 	name.clear();
-	TempState temp_state = mem::temp_push();
+	PoolState temp_state = mem::temp_push();
 	defer mem::temp_pop(temp_state);
 	foreach(unit : tests)
 	{