Missing contract test coverage for GetArtifactVersion()

[w1t]

The new func (s *gcsService) GetArtifactVersion(ctx context.Context, req *artifact.GetArtifactVersionRequest) method does not appear to be covered by the contract tests yet.

adk-go/artifact/request_validation_test.go

Line 329 in b8eb8c5

func TestGetArtifactVersionRequest_Validate(t *testing.T) {

It would be useful for the contract tests to define which ArtifactVersion fields are required across backends, which are optional, and whether backend-specific omissions are allowed.

[indurireddy-TF]

Hi @baptmont @mazas-google @dpasiukevich ! this is missing. Can we add the test cases for GetArtifactVersion and open a PR?