Add generic type parameter for Round state

[giokaxo]

Summary

• Add generic type parameter <T = unknown> to Round, PlayResponse, AuthenticateResponse, Client, and RGSClient
• Allows consumers to specify the type of round.state instead of it being hardcoded to unknown
• Fully backwards compatible — defaults to unknown when no type argument is provided

Problem

The Round.state field was typed as unknown, requiring consumers to manually cast the state on every access:

const client = RGSClient({ url: '...' });
const res = await client.Play({ amount: 100, mode: 'base' });
const state = res.round.state as MyGameState; // manual cast needed every time

Solution

The generic parameter flows end-to-end from RGSClient<T> through Client<T>, AuthenticateResponse<T>, PlayResponse<T>, and Round<T>:

type MyGameState = { reels: number[][]; multiplier: number };

const client = RGSClient<MyGameState>({ url: '...' });
const res = await client.Play({ amount: 100, mode: 'base' });
res.round.state.reels;      // number[][] — fully typed
res.round.state.multiplier;  // number — fully typed

Test plan

• Verify the build completes without type errors
• Confirm existing consumers without type arguments still compile (backwards compatible via = unknown default)
• Test that specifying a type argument correctly narrows round.state

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