Replace usages of "any" with "unknown" for 2.0.0

[grumd]

unknown is a safer alternative to any. SWR defaults to any for data and error, error being the bigger problem as its type can't be inferred.

The problem with any is that I can do error.foo.bar() and get a runtime error. This is not the best practice for properly typed code. unknown forces you to do the required type checks (e.g. error instanceof Error) before working with the variable.

That's also why Typescript since 4.0 requires you to specify catch (error: any) or catch (error: unknown) instead of defaulting to any to allow users to opt into a more type-safe option. And since 4.4 there's also a useUnknownInCatchVariables option to simply default to unknown.

I feel like SWR lags behind these Typescript trends and causes issues with recommended eslint rules like this one https://typescript-eslint.io/rules/no-unsafe-assignment/

Can we replace any with unknown in SWR types for 2.0.0?