Fix automatic size hint on uploads

[JustAnotherArchivist]

When uploading without a size hint (via headers or --size-hint), a x-archive-size-hint header is added automatically. However, prior to this commit, the value was the individual file size on each file's PUT request. This effectively made the size hint useless because it does not, in fact, provide a size hint for the total item size to the S3 backend at item creation time.

Notes on detailed changes to implement this:

• Rename internetarchive.utils.recursive_file_count to recursive_file_count_and_size, adding a wrapper for backwards compatibility
• Add support for paths (rather than only file-like objects) to internetarchive.utils.get_file_size
• Add a internetarchive.utils.is_filelike_obj helper function
• Fix a bug introduced by 62c85133090e21659f09964fedd4c18ae4a27483 where total_files would never be None and so recursive_file_count was never called, possibly leading to incorrect derive queueing.
• Add tests for the fixed behaviour

[jjjake]

Looks great. Thanks again @JustAnotherArchivist.