gh-155907: Raise OSError and KeyboardInterrupt when reading marshal data - #155909

r_string(), r_byte() and PyMarshal_ReadLastObjectFromFile() did not check ferror() nor call PyErr_CheckSignals(), so a genuine I/O error or a read interrupted by Ctrl-C was reported as EOFError, as if the file had simply ended.

>>> import _testcapi, os
>>> os.mkdir('d')
>>> _testcapi.pymarshal_read_object_from_file('d')
EOFError: EOF read where object expected      # before
IsADirectoryError: [Errno 21] Is a directory  # after

The documentation of these functions listed only EOFError, ValueError and TypeError, which was inaccurate even before this change (MemoryError is raised when the read buffer cannot be allocated), so the lists are removed.

• Issue: marshal reports EOFError for I/O errors when reading from a FILE* #155907