Unable to rotate password without overriding internal HTTP infrastructure

---

### Package
ClickHouse.Driver

### Package Version
| Package Name | Version |
| ------------ | ------- |
| ClickHouse.Driver | 1.2.0 |

### Runtime Version
net10.0

### Description
Unfortunately, I was unable to compile the source code locally, so I'm filing an issue instead of a full-blown pull request.

### The problem
There is a need to periodically rotate the password used for authentication. The password may be different each time a new connection is opened. However, the current driver API does not provide a way to supply or refresh credentials at connection time — they are set once during initial setup and cannot be changed without creating a new driver instance.

This forces us to implement a workaround by overriding internal HTTP infrastructure. Specifically, we had to create a custom `HttpClientFactory` with a custom `HttpMessageHandler` that overwrites the `Authorization` header inside `SendAsync`/`Send` on every request:

```csharp
request.Headers.Authorization = new AuthenticationHeaderValue(
"Basic",
Convert.ToBase64String(Encoding.UTF8.GetBytes($"{username}:{currentPassword}")));
```

The driver should support password rotation natively, without requiring users to patch internal HTTP client factories and message handlers.

### The solution
Add a mechanism to the driver that allows one of the following:
1. Provide a credentials provider (callback / delegate) that is invoked every time a connection is established or a request is made.
2. At minimum, expose a way to override the authentication logic without patching internal factory classes.

### Steps to Reproduce
1. Configure the driver with a set of credentials.
2. Rotate the password externally.
3. Try to open a new connection or execute a query with the new password.

### Expected Result
The driver should be able to use the updated password without recreating the entire driver instance.

### Actual Result
The driver uses the old password. The only way to use a new password is to either recreate the driver instance or apply the workaround with a custom HTTP handler.

### Additional Context
Password rotation is a common security requirement in production environments. Having to recreate the entire driver instance or patch internal infrastructure adds unnecessary complexity and is error-prone.

Start by tracing how the driver API stores credentials and how its internal HttpClientFactory and HttpMessageHandler set authentication, including the SendAsync/Send paths mentioned in the issue. Compare connection-time and request-time credential needs, then define completion as password rotation working without recreating the driver or overriding internal HTTP infrastructure.

Written by the indexing model from the issue text.