Use typing.TypedDict for decoded json data.

[TheCommCraft]

The typing.TypedDict allows for typing specific keys of dicts and would improve code readability.

Though useful for creating scratchattach, this still isn't as urgent as other issues.

• [x] Session updater
• [x] User updater
• [x] Studio updater
• [ ] Project updater
• [ ] Forum updater
• [ ] ...