Add py.typed marker file

[sersorrel]

What do these changes do?

Type checkers look for a py.typed file before doing type-checking on libraries imported by other code (see PEP 561).

Adding include_package_data=True to setup.py means that the marker file will also be included in bdists (i.e. wheels), not just sdists.

Are there changes in behavior for the user?

Users who use mypy for type-checking will now be able to make use of the type hints in aiohttp-cors, i.e. if they are currently getting an error which looks like this:

error: Cannot find module named 'aiohttp_cors'

they will stop getting this error.

Related issue number

none

Checklist

• [x] I think the code is well written
• [ ] Unit tests for the changes exist – n/a
• [ ] Documentation reflects the changes – n/a
• [ ] Add a new news fragment into the CHANGES folder – what CHANGES folder?
  • name it <issue_id>.<type> (e.g. 588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the PR
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: Fix issue with non-ascii contents in doctest text files.

[asvetlov]

Typing marker is useless until we test typing correctness by mypy tool along with unit tests run.

I know, now the library doesn't pass mypy. Would you fix it as well?

[sersorrel]

I started fixing some of the annotations, but since I'm not sure how the library works I wasn't sure how to fix the rest of them. I'll have another look at the remaining problems (which are mostly where something returns an AbstractResource, but a particular subclass (or a Union[Resource, StaticResource, ResourceRoute]) is expected) later.

[sersorrel]

Remaining issues:

• the signature of ResourcesUrlDispatcherRouterAdapter.add_preflight_handler is not compatible with the superclass AbstractRouterAdapter.add_preflight_handler (webview argument):

  https://github.com/aio-libs/aiohttp-cors/blob/73510a3a9212afd1d3740fd8b2feba63a1dcfe13/aiohttp_cors/urldispatcher_router_adapter.py#L137-L141

  https://github.com/aio-libs/aiohttp-cors/blob/73510a3a9212afd1d3740fd8b2feba63a1dcfe13/aiohttp_cors/abc.py#L53-L56

• several functions (is_cors_for_resource, add_preflight_handler, set_config_for_routing_entity) expect a particular kind of resource, but are passed an Optional[AbstractResource], which usually comes from aiohttp's type hints

• _request_resource claims that web.AbstractRoute/web.ResourceRoute returns a web.Resource, but the aiohttp type hints don't agree

I think the last two issues might require modifications to aiohttp, and I don't know how you want to handle the first issue (presumably just add an ignored webview argument to ResourcesUrlDispatcherRouterAdapter.add_preflight_handler?). Personally I think the typing issues here are no greater than the typing issues with aiohttp itself at this point.

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