addSubscription TS signature is incorrect

[campbellcole]

The signature for the client.addSubscription function cause valid parameters to error out, and causes "valid" parameters to throw runtime errors.

Given the following subscription in the Router:

router
    .subscription("logs", |s| {
        s(|_, test: ()| LogExportLayer::add_client())
    });

the following TS will throw a TypeScript error:

client.addSubscription(["logs"], { ... });
// Argument of type '["logs"]' is not assignable to parameter of type '["logs", []]'.

and if the () type is replaced with, say, String: Argument of type '["logs"]' is not assignable to parameter of type '["logs", [string]]'.

The fix is relatively simple and I will submit a pull request shortly.

[oscartbeaumont]

Thanks! Should be fixed!