Add ChangesSummary to SessionChatSummary in multiple clients

[Ladislau Szomoru (lszomoru)]

This pull request introduces a new optional field, changes?: ChangesSummary, to the SessionChatSummary protocol. This change allows per-chat counts to be communicated to list clients without requiring new actions or subscriptions, leveraging the existing root/sessionSummaryChanged mechanism.

Changes made:

• Field Addition: Added changes?: ChangesSummary to SessionChatSummary in the TypeScript client.
• Generated Code: Updated client models for Rust, Kotlin, Swift, Go, and .NET. The TypeScript client generated sources remain unchanged due to the optional nature of the new field.
• Test Fixture: Created a new round-trip test case to ensure the integrity of session totals and per-chat counts.
• Changelog: Added a new entry to document this change across the specification and all clients.
• Documentation: No additional documentation changes were necessary, as the new field is self-explanatory in the context of the existing protocol.

Test Results:

• All tests for Go, Rust, and TypeScript clients passed successfully.
• Swift library builds successfully, but tests could not be executed due to environment limitations.
• Kotlin tests were not run due to the absence of a Java runtime.
• One .NET test failed, but it is unrelated to the changes made.

This update enhances the protocol's functionality while maintaining backward compatibility.