Add support for `HashableMessage` in `signMessage`

[helciofranco]

Update signMessage to accept HashableMessage instead of just string, to match the latest SDK (v0.100.0) changes.

Links:

• https://github.com/FuelLabs/fuel-connectors/blob/main/packages/fuel-wallet/src/FuelWalletConnector.ts#L184-L192
• https://github.com/FuelLabs/fuels-ts/blob/f9c31e43d93c62909ac500579a1e40f54070746f/packages/account/src/connectors/fuel-connector.ts#L166-L177
• https://github.com/FuelLabs/fuels-ts/blob/f9c31e43d93c62909ac500579a1e40f54070746f/packages/hasher/src/hasher.ts#L66-L80