fix: handle proto.Message and repeated fields in format_output_value

[danishashko]

Fixes #25

format_output_value() was only handling proto.Enum types. When a query returns fields like responsive_search_ad.headlines or responsive_search_ad.descriptions, the value is a RepeatedCompositeContainer (a list of proto messages), which isn't JSON-serializable as-is.

Changes:

• Added handling for proto.Message values using proto.Message.to_dict()
• Added recursive handling for list and tuple values so nested repeated fields are also serialized correctly
• Existing behavior for proto.Enum and plain scalars is unchanged

This lets the search tool handle RSA headlines/descriptions and other repeated composite fields without crashing.

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[Raibaz]

Thanks for looking into this!

Would you be able to provide test coverage along with this change? See my comments to #26