Strongly typed server response error

### Use case
https://github.com/ClickHouse/clickhouse-rs/pull/426

### Describe the solution you'd like

Change `Error::BadResponse(String)` to `Error::ServerError(ServerError)` where `ServerError` is a new struct:

```rust
pub struct ServerError {
// Expose these fields as getters
code: u32,
name: Option,
message: String,
}
```

This should just be a loud breaking change so users know it happened. #426 suggested adding this as a new variant alongside `BadResponse(String)`, but that would change existing error handling in a way that is unintuitive and could break existing deployments.

There is still the possibility of failing to parse the response, however. I think we could return that as `Error::Other()` instead.

### Describe the alternatives you've considered

### Additional context

Start by locating the existing Error::BadResponse(String) definition and its response-parsing call sites, then read the linked PR #426 for the prior approach. Trace how server error code, name, and message are currently handled. Done means the error exposes the requested typed ServerError data, preserves the intended parse-failure behavior, and passes the relevant existing tests.

Written by the indexing model from the issue text.