[Feature request]: Cast class fields

If I have any class, and I get a warning like the following on a function that is being given a class field as a parameter (e.g., tohex(class_name.class_field)):

Cannot assign `string|integer` to parameter `integer`.
[Lua Diagnostics.: param-type-mismatch]

Is there already a way to cast this class field? If not, could it be implemented?

When trying to cast something like ---@cast group.foreground -string, I get the warning:

Unknown type conversion variable `{}`.
[Lua Diagnostics.: unknown-cast-variable]

Start by tracing the unknown-cast-variable and param-type-mismatch diagnostics described in the issue, then inspect how casts currently resolve variables and class fields. Done means a cast such as ---@cast group.foreground -string is accepted and removes the reported type warning when the field is passed to an integer-only function.