fix(client-gen): implement client-side extends with service accessors

[m62624]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @m62624, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a significant enhancement to the client-side code generation by implementing the extends keyword for services in the IDL. This feature allows for better modularity and reusability of service definitions. Alongside this, the structure of mock object generation has been refactored to be more granular and organized, residing within individual service modules. The changes also include refinements in type handling, such as supporting external types and improving type path resolution, leading to cleaner and more efficient generated client code.

Highlights

• Client-side extends Implementation: The client-gen tool now supports the extends keyword in IDL definitions, allowing services to inherit functionality from other services. This generates accessor methods on the client for the extended services, as demonstrated by the Dog service extending WalkerService and MammalService.
• Refactored Mock Generation: Mock modules are now generated within each service's module (e.g., service_name::mockall) instead of a single top-level mockall module. This improves code organization and reduces potential naming conflicts for generated mocks.
• Improved Type Handling: The client generator now supports specifying external types (e.g., NonZeroU8, NonZeroU32), preventing redundant code generation for types already defined elsewhere. Additionally, type path resolution for Result and Option within generated io modules has been improved, and program-level types are now relocated to their primary service modules.
• Updated Demo and Tests: The demo_client IDL and associated tests have been updated to showcase the new extends functionality, demonstrating how to interact with extended services through their accessors.

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[gemini-code-assist]

Code Review

This pull request implements the extends feature for services on the client-side, which is a great addition. The implementation of service accessors for extended services within the service client itself looks correct. The refactoring of the generator to move mock generation into per-service modules is also a good improvement for modularity.

However, I've identified a couple of issues in the generator logic:

1. The generator incorrectly creates top-level accessors on the program client for services that are not exported by the program but are used in extends.
2. The path resolution for types in function signatures (especially in Result types) is not always correct, as it doesn't seem to account for types defined in different scopes (e.g., program-level vs. service-level).

I've added specific comments with suggestions for these issues.