Add type annotation to the tracing and signals

[YuvalPruss]

What do these changes do?

Add typing for the aiohttp/tracing.py and the aiohttp/singals.py.

Are there changes in behavior for the user?

No, these are just hints for the type checkers.

Related issue number

#1749

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> for example (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]

Signal is inherited from FrozenList.

Since FrozenList is a generic class the Signal is generic too, e.g. Signal[Callable[['Application'], Awaitable[None]]].

Please fix corresponding types for signal variables.

[dbohomiakov]

@YuvalPruss are you going to finish pr? Cause I have ready pr for tracing.py file.

[asvetlov]

Outdated by #3343

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a [new issue] for related bugs.
If you feel like there's important points made in this discussion, please include those exceprts into that [new issue].
[new issue]: https://github.com/aio-libs/aiohttp/issues/new