Fix python compiler generated all_structs with type_hints

[fishy]

Currently with type_hints enabled, we do not explicitly declare the type of generated all_structs. It's meant to be a list of different types, but that will cause problems, as the generated code is usually like this:

all_structs = []
...
all_structs.append(Type1)
...
all_structs.append(Type2)
...

The first append infers the type of all_struct to be list[Type1], so mypy would start complaining from the 2nd append as the type is unexpected.

Explicitly declare all_struct to be list[typing.Any] instead, which fixes the issue.

[fishy]

~NOTE: this fixes a bug in the new feature added to the 0.21.0 release, so it should ideally be part of the 0.21.0 release.~ changing this PR to target master branch (next release) instead.

[SalomonSmeke]

Thank You! One can skip type checking the import or get around this with implicit Any but its much nicer to have this declared :)

[salomon-smekecohen]

Working on adding more to this.