Unexpected batch behavior

### The problem

If we do a batch request where the response array contains a response object which is an error, `ElectrumClient` will return `Err(Error::Protocol)` and the response objects will be discarded. This is not ideal as in most instances, we still want the response objects.

For example, a single request to method `blockchain.transaction.get` may return an response object with error if the transaction does not exist. Doing a batch of `blockchain.transaction.get` requests where we have a single transaction that the electrum server is not aware of (yet), will result in us not seeing any of the other response objects.

**This is the current API for a batch request**

https://github.com/bitcoindevkit/rust-electrum-client/blob/129081999ce96f1ed33877a2aecad4e2550764f3/src/raw_client.rs#L697

### Proposed solution

```rust
fn batch_call(&self, batch: &Batch) -> Result, Error> { todo!() }

pub enum RawResponse {
/// Instead of returning `Err(Error::Protocol)`, we have this.
Error { code: i32, message: String, data: Option },

/// The successful result, as usual.
Result(serde::Value),
}
```

The `RawResponse` can be used to transform into a non-raw response depending on the method invoked.

For example, `client.transaction_get()` can return `Result, Error>`.

### Questions

- The electrum server API docs does not provide error codes for error responses. Is there a standard for these? For example, if a transaction is not found.

### Reference

- https://www.jsonrpc.org/specification
- https://electrumx-spesmilo.readthedocs.io/en/latest/protocol-methods.html#blockchain-transaction-get