feat: improve error handling in interpreter

Introduced better error handling in the Deuthon interpreter loop by wrapping the code execution in a try-except block to catch and print exceptions using `traceback`. This change also updates the interpreter to only print output when `eval` returns a non-None result, enhancing usability and feedback for the user. The addition of `traceback` provides users with more insightful error messages, helping to debug incorrect German code inputs more effectively.

src/deuthon/interpreter.py

@@ -1,11 +1,19 @@
 from .transformer import parse_german_code
 
+import traceback
+
 def interpreter():
     while True:
         try:
-            german_code = input('>>> ')
+            german_code = input(">>> ")
         except EOFError:
             break
 
+        try:
             python_code = parse_german_code(german_code)
-        exec(python_code)
+            result = eval(python_code, globals())
+
+            if result is not None:
+                print(result)
+        except Exception:
+            print(traceback.format_exc())