Fix len parameter handling: Unit tests for gRPC and session

[batzuu]

• [x] This contribution adheres to CONTRIBUTING.md.
• [ ] ~~I've updated CHANGELOG.md if applicable.~~
• [x] I've added tests applicable for this pull request

What does this Pull Request accomplish?

This PR is in the continuation of PR: Fixing size parameter handling and aims to add unit test for gRPC and session for the new nifake function added in the earlier PR.

• Adds necessary changes to enable gRPC calls for the new test method MultipleArraysDifferentSize in nifake.proto.
• Adds corresponding generated files, and tests (covered in testing section).

List issues fixed by this Pull Request

Adds to the validation for changes added to fix Issue 2137: Fix size parameter handling for functions with parameters referencing multiple size parameters.

What testing has been done?

• Unit test test_multiple_arrays_different_size added in nifake's test_grpc.py and test_session.py for validation.