fix: error out if multiple wheels with the same name are produced

We shouldn't silently overwrite wheels that are produced in the same run that have the same filename, as this implies a misconfiguration.

cibuildwheel/util.py

@@ -373,6 +373,20 @@ class NonPlatformWheelError(Exception):
         super().__init__(message)
 
 
+class AlreadyBuiltWheelError(Exception):
+    def __init__(self, wheel_name: str) -> None:
+        message = textwrap.dedent(
+            f"""
+            cibuildwheel: Build failed because a wheel named {wheel_name} was already generated in the current run.
+
+            If you expected another wheel to be generated, check your project configuration, or run
+            cibuildwheel with CIBW_BUILD_VERBOSITY=1 to view build logs.
+            """
+        )
+
+        super().__init__(message)
+
+
 def strtobool(val: str) -> bool:
     return val.lower() in {"y", "yes", "t", "true", "on", "1"}