Add type-hinting metadata to package build

[rjdbcm]

This PR adds a py.typed file and Typing :: Typed classifier to support static typechecker use by modules importing webui2.

Known Issues

mypy shows 2 fails in a platform specific logic branch but this appears to be a mypy issue

load_library.py:75: error: Module has no attribute "add_dll_directory"  [attr-defined]
load_library.py:79: error: Module has no attribute "add_dll_directory"  [attr-defined]

[AlbertShown]

Thank you @rjdbcm for this PR.

LGTM.

Waiting for @SageCreations

[SageCreations]

Looks good, I'm adding a fix for send_raw function, that ups the version to 2.5.2, this will be included in that release.