SCP-3331 Fixed error handling for transaction balancing in PAB.

[bwbush]

The Cardano.Wallet.LocalClient.runClient' function erroneously rethrows errors it catches instead of returning them via pure . Left, as required by its type signature. The errors are not handled and end up killing the thread that handles the contract instance. This change successfully passes the Marlowe test https://github.com/input-output-hk/marlowe-cardano/blob/sprint-52/marlowe-cli/test/test-wallet-failure.yaml.

(In general, I recommend reviewing the PAB codebase for similar re-throwing problems and for forkIOs that aren't guarded against its thread dying because of an uncaught exception.)

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[sjoerdvisscher]

Thanks, nice catch!