Added useful error message in case Register Observer is not supported

Author: fjwillemsen

kernel_tuner/observers/register.py

@@ -7,6 +7,10 @@ def __init__(self) -> None:
         super().__init__()
 
     def get_results(self):
+        try:
+            registers_per_thread = self.dev.num_regs
+        except AttributeError:
+            raise NotImplementedError(f"Backend '{type(self.dev).__name__}' does not support count of registers per thread")
         return {
-            "num_regs": self.dev.num_regs
+            "num_regs": registers_per_thread
         }