Consider implementing server-side md5

[bkanuka]

GCP can compute the md5 hash server-side: https://googleapis.dev/python/storage/latest/blobs.html#google.cloud.storage.blob.Blob.md5_hash

hash() is not typically implemented in pyfilesystem according to: https://docs.pyfilesystem.org/en/latest/implementers.html#helper-methods however, in this case it could be argued that there is a performance benefit to getting the hash from the server rather than downloading+computing it client-side.

Note that this only works for md5 and crc32c. Therefore the implementation could just fallback to the parent class otherwise. An implementation might look like this (complelely untested):

def hash(self, path, name):
    if name.lower() == 'md5':
        _path = self.validatepath(path)
        _key = self._path_to_key(_path)
        blob = self._get_blob(_key)
        if not blob:
            raise errors.ResourceNotFound(path)
        return blob.md5_hash
    else:
        return super().hash(self, path, name)