HDDS-14562. Test if proto 3 SCM request can be parsed by proto 2

[Russole]

What changes were proposed in this pull request?

HDDS-10481 introduced TestSCMRatisProtocolCompatibility with a test verifying that proto2 requests can be parsed by proto3.
This JIRA extends that coverage by adding the reverse test, ensuring that proto3 requests can also be parsed by proto2.

• Added testProto3RequestCanBeParsedByProto2 to verify that requests encoded with proto3 can be successfully parsed by the legacy proto2 schema.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-14562

How was this patch tested?

• All CI checks passed.
  • https://github.com/Russole/ozone/actions/runs/21774673841
• Added unit tests and all tests pass.

[szetszwo]

@Russole , thanks for working on this!

• Let's add a test for RequestType as below

  @Test
  public void testRequestType() {
    for (Proto2SCMRatisProtocolForTesting.RequestType proto2 : Proto2SCMRatisProtocolForTesting.RequestType.values()) {
      final SCMRatisProtocol.RequestType proto3 = SCMRatisProtocol.RequestType.valueOf(proto2.name());
      assertEquals(proto3.getNumber(), proto2.getNumber());
      assertEquals(proto3.toString(), proto2.toString());
    }
  }

• Also, let's make the tests to run with random values. For proto2-to-proto3 tests, see https://issues.apache.org/jira/secure/attachment/13080703/TestSCMRatisProtocolCompatibility.java

• Could you add similar proto3-to-proto2 tests?