Add DescribeConsumer support in Topic SDK

[vgvoleg]

Implements DescribeConsumer API call for Topic SDK, allowing users to get detailed information about a topic's consumer including partition stats and consumer offsets.

Closes #713

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What is the current behavior?

Issue Number: N/A

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Pull request overview

Adds support for the TopicService DescribeConsumer API in the Python Topic SDK so users can fetch consumer details (including optional per-partition stats and location info).

Changes:

• Added describe_consumer() to both async and sync Topic clients.
• Introduced new public request/response types for DescribeConsumer, plus corresponding grpcwrapper parsing/to_public conversions.
• Added control-plane tests covering DescribeConsumer basics and offset/stat assertions.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
ydb/topic.py	Exposes describe_consumer() on async/sync clients and exports TopicConsumerDescription.
ydb/_grpc/grpcwrapper/ydb_topic_public_types.py	Adds DescribeConsumer request params and public result dataclasses for consumer/partition stats and location.
ydb/_grpc/grpcwrapper/ydb_topic.py	Implements protobuf-to-public conversions for DescribeConsumerResult, PartitionConsumerStats, and PartitionLocation.
ydb/_apis.py	Registers DescribeConsumer method name constant for TopicService calls.
tests/topics/test_control_plane.py	Adds async/sync tests for DescribeConsumer, including stats and committed offsets.

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Pull request overview

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Pull request overview

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