Implement IComparable for Offset and Partition

[Dreamescaper]

Today I have realized that the code like this fails:

messages.Max(message => message.Offset);

Despite having < or > operators, Offset does not implement IComparable, so this code fails with an exception:

  Message: 
System.ArgumentException : At least one object must implement IComparable.

  Stack Trace: 
Comparer.Compare(Object a, Object b)
ObjectComparer`1.Compare(T x, T y)
Enumerable.Max[TSource,TResult](IEnumerable`1 source, Func`2 selector)

I decided to submit a PR fixing that.

Checklist

• Contains customer facing changes? (Interface implemented)
• Including API/behavior changes
• Did you add sufficient unit test and/or integration test coverage for this PR?

[Copilot]

Pull Request Overview

This PR adds IComparable<T> implementation to the Offset and Partition structs, enabling use of LINQ operations like Max() and Min() that require comparable types.

Key changes:

• Implements IComparable<Partition> and IComparable<Offset> interfaces
• Adds CompareTo methods that delegate to the underlying Value property's comparison
• Includes comprehensive unit tests for the new comparison functionality

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/Confluent.Kafka/Partition.cs	Adds IComparable<Partition> interface and CompareTo method implementation
src/Confluent.Kafka/Offset.cs	Adds IComparable<Offset> interface and CompareTo method implementation
test/Confluent.Kafka.UnitTests/Partition.cs	Adds unit tests verifying CompareTo behavior for equal, greater, and lesser values
test/Confluent.Kafka.UnitTests/Offset.cs	Adds unit tests verifying CompareTo behavior for equal, greater, and lesser values

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