Clarify correlation hook parameter documentation

[Copilot]

The documentation for register_correlation_hook in snapshooter.py was ambiguous about the hook's three parameters, making it unclear they were separate arguments rather than a single description.

Changes:

• Updated docstring to explicitly list the three parameters: entity_type (str), current_values (dict, including linked entities), and master_record (dict)

Before:

hook: `hook` callable should expect entity type as str
    and its current values, including linked entities, as dict;
    and its master record as dict.

After:

hook: `hook` callable should expect three parameters:
    entity_type (str), current_values (dict, including linked entities),
    and master_record (dict).

This aligns with the actual function signature: Callable[[str, dict, dict], Union[None, list[DataPointTask]]]

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