Minor Batch Enhancements

[liquizard]

Status	Type	⚠️ Core Change
Ready	Feature/Bug	No (minor changes)

Problem

Minor enhancements to Batch requests + Token Wallets

• load mulltiple TokenWallet instance via the batch composer

            // init batch
            var batch = new SolanaRpcBatchWithCallbacks(client);
            batch.AutoExecute(BatchAutoExecuteMode.ExecuteWithFatalFailure, 50);

            // request multilpe wallets
            var walletPromise1 = TokenWallet.LoadAsync(batch, tokens, pubkey1);
            var walletPromise2 = TokenWallet.LoadAsync(batch, tokens, pubkey2);
            var walletPromise3 = TokenWallet.LoadAsync(batch, tokens, pubkey3);
            var walletPromise4 = TokenWallet.LoadAsync(batch, tokens, pubkey4);
            batch.Flush();

            // enjoy your wallets
            var wallet1 = walletPromise1.Result;
            ...

Other changes (e.g. bug fixes, small refactors)

• added overload to TokenWalletFilterList
• bugfix Batch.Flush() on empty batches