Add explicit type validation for `settings` in configuration loading

[sourcery-ai]

There is currently a potential bug risk in the handling of the settings configuration parameter. The code assumes that settings is always a dictionary and passes it directly to update(). If a user provides a non-dict value (e.g., a list or string) in their config file, this will result in a runtime error, but the resulting stack trace may be deep within the codebase and not clearly indicate that the root cause is an invalid type for settings.

Proposed Solution:

• Add an explicit type check for settings when loading the configuration. If settings is not a dictionary, raise a clear and descriptive error (e.g., ConfigurationError) that tells the user exactly what went wrong and how to fix it.
• Alternatively, consider defaulting to an empty dict if the type is incorrect, but raising an error is preferable for clarity and to avoid silently swallowing misconfigurations.

Example Implementation:

settings = self._ch_ctl_config.get("settings", {})
if not isinstance(settings, dict):
    raise ConfigurationError(
        f"Invalid type for `clickhouse.settings`: expected dict, got {type(settings).__name__}"
    )

Long-term Suggestion:

• Consider using a strongly-typed configuration library such as Pydantic to enforce config types at load time. This would provide even more robust validation, but is likely out of scope for the current PR.

Action Items:

1. Add an explicit type check for settings in the configuration loading logic.
2. Raise a clear error if the type is incorrect.
3. Optionally, create a follow-up issue to investigate using Pydantic or similar for full config validation.

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I created this issue for @Alex-Burmak from #248 (comment).

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