Update dataclass documentation for new __eq__ behavior in 3.13 and add tests

Author: Aniketsy

Doc/library/platform.rst

@@ -56,14 +56,6 @@ Cross platform
    Returns the machine type, e.g. ``'AMD64'``. An empty string is returned if the
    value cannot be determined.
 
-   .. note::
-
-      The output of :func:`platform.machine` is system-dependent and may differ
-      in casing and naming conventions across platforms. For example, on Apple
-      Silicon macOS it may return ``'arm64'`` (lowercase), while on Windows-on-ARM
-      it may return ``'ARM64'`` (uppercase). If you need consistent results,
-      normalize the output in your code.
-
 
 .. function:: node()