Consider using proper type annotations

[arminru]

          I think the "proper" solution would be to switch from legacy `# type:` comments to using actual annotations.

For example, instead of:

mandatory_keys = ("id", "brief")  # type: Tuple[str, ...]

use:

mandatory_keys: Tuple[str, ...] = ("id", "brief")

And since we probably rely on 3.9+ anyway, one could even use the built-in tuple support for generic arguments and drop the import, using:

mandatory_keys: tuple[str, ...] = ("id", "brief")

Not a blocking comment, just a suggestion.

Originally posted by @Oberon00 in #231 (comment)

[lmolkova]

Given that we're sunsetting build-tools (#322) and it's not applicable to weaver, I'm going to close it