Exclude non-retryable exceptions from retry mechanism in block_until_done

[Copilot]

The @retry_on_failure decorator on block_until_done was retrying all exceptions, including authentication failures, permission errors, and invalid task IDs that will never succeed on retry.

Changes

New exception types (utils/exceptions.py):

• AuthenticationError - auth failures (401)
• ProxmoxPermissionError - permission denied (403)
• InvalidTaskError - invalid/missing task IDs (404)

Selective retry logic (utils/utils.py):

• Decorator now only retries: ProxmoxAPIError, ConnectionError, TimeoutError
• Exception handler uses Proxmoxer's native types (ProxmoxerAuthenticationError, ResourceException) with HTTP status code inspection instead of string matching
• Non-retryable exceptions propagate immediately; retryable exceptions go through retry flow

@retry_on_failure(
    max_attempts=3,
    delay=2.0,
    exceptions=(ProxmoxAPIError, ConnectionError, TimeoutError)  # Only these retry
)
def block_until_done(...):
    try:
        data = prox.nodes(node).tasks(task_id).status.get()
    except ProxmoxerAuthenticationError as e:
        raise AuthenticationError(...)  # Won't retry
    except ResourceException as e:
        if e.status_code == 403:
            raise ProxmoxPermissionError(...)  # Won't retry
        elif e.status_code == 404:
            raise InvalidTaskError(...)  # Won't retry
        else:
            raise ProxmoxAPIError(...)  # Will retry

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