Increase modal-client type coverage

[savarin]

This is an umbrella issue created to add types to modal-client.

We expect changes to be made in two stages:

1. Expand type coverage to allow mypy to pass beyond the existing check on .pyi stubs.
2. Implement strict type checking, as well as remove Any and type ignores (where possible) above.

Existing dependency tree as generated with pydeps and the following .pydeps file.

[pydeps]
pylib = False
exclude =
    aiohttp
    aiostream
    aiostream
    asgiref
    click
    cloudpickle
    dotenv
    fastapi
    grpclib
    ipykernel
    rich
    synchronicity
    tblib
    toml
    typer
    typing_extensions
    watchfiles

[zsiegel92]

Hey @savarin or @freider FYI I opened this related PR and filed this related issue.

If you have any availability to chip away at this I'll be so grateful! 🙏 Thanks!