Adds 2 new constants to FileSizeLimit if you're running in local mode.

Didn't go with math.inf for FILESIZE_DOWNLOAD_LOCAL since that's a float which can't be converted to int. So went with sys.maxsize

Checklist for PRs

• Added .. versionadded:: version, .. versionchanged:: version or .. deprecated:: version to the docstrings for user facing changes (for methods/class descriptions, arguments and attributes)
• Created new or adapted existing unit tests
• Documented code changes according to the CSI standard
• Added new classes & modules to the docs and all suitable __all__ s