Support digest function in GrpcStore

[asr2003]

Description

• Updated ResourceInfo to default digest_function to sha256 if not provided.
• Ensured backward compatibility for existing functionality.

Fixes #1325
/claim #1325

Type of change

Please delete options that aren't relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please also list any relevant details for your test configuration
Tests added

Checklist

• [] Updated documentation if needed
• Tests added/amended
• bazel test //... passes locally
• PR is contained in a single commit, using git amend see some docs

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This change is 

[MarcusSorealheis]

Please do not open up PRs that do not adhere to the checklist, unless they do not impact NativeLink.

[asr2003]

The failed check before isn't known what it is failed for seems a deployment failure! Hopefully the deployments succeeded now

[aaronmondal]

+@allada @MarcusSorealheis What do we do about test coverage here? The grpcStore currently has no tests 😅 https://tracemachina.github.io/nativelink/coverage/build/source/nativelink-store/src/grpc_store.rs.html

@asr2003 I think it should be fine if we just cover the changed parts, i.e. unit tests for the read, has_with_results and is_supported_digest_function, and only tests that trigger the branches that you added (i.e. tests that force the new error handling and check that they're actually hit).

Reviewable status: 0 of 2 LGTMs obtained, and 0 of 2 files reviewed (waiting on @allada)

[asr2003]

Sure! I will add tests to ensure the branch coverage.

[asr2003]

@aaronmondal To validate the is_digest_function , I have added the tests and grpc_ store unit tests for read and has_with_results I have mocked store and I am not sure there in right way but the changes added here of read will refelected in the https://github.com/TraceMachina/nativelink/blob/main/integration_tests/simple_remote_execution_test.sh
which I guess GRPCStore runs underhood and I have also faced before some test fail from it of same read fail when I have worked on it and which I used for evaluation of this PR changes.

Here's what I have mocked for and looking part of unit test but fails :)

    async fn test_read_with_valid_digest_function() {
        let config = Retry::default();

        let mock_grpc_store = GrpcStore {
            instance_name: "test".to_string(),
            store_type: nativelink_config::stores::StoreType::cas,
            retrier: Retrier::new(
                Arc::new(|_| Box::pin(sleep(Duration::from_secs(0)))),
                Arc::new(|delay: Duration| delay),
                config,
            ),
            connection_manager: ConnectionManager::new(
                vec!["test-endpoint"]
                    .into_iter()
                    .map(|endpoint_str| {
                        let grpc_endpoint = GrpcEndpoint {
                            address: endpoint_str.to_string(),
                            tls_config: None,                
                            concurrency_limit: Some(1),       
                        };
                        tls_utils::endpoint(&grpc_endpoint).unwrap()
                    })
                    .collect::<Vec<_>>(),
                1,
                1,
                Retry::default(),
                Arc::new(|_| Duration::from_secs(0)),
            ),
        };

        let read_request = ReadRequest {
            resource_name: "resource-sha256".to_string(),
            read_offset: 0,
            read_limit: 10,
        };

        let result = mock_grpc_store_.read(read_request).await;
        assert!(result.is_ok(), "Read should succeed with supported digest function");
    }

Correct me if I am wrong in mocking GRPC Store for unit tests