Add compatibility with protobuf 28 (backport #541)

[mergify]

🎉 New feature

Adds compatibility with the Google Protocol Buffers v28.

Summary

Basically, rules for message down casting have been changed in protobuf and this PR modifies the way protobuf is used for downcasting.

Protobuf does not allow to use google::protobuf::internal::DownCast function to downcast message types with concepts enabled in version 28 (see port.h file in this diff). When compiling custom packages which depend on the gz-transport with C++ concepts enabled, there will be compile-time errors, if RepHandler::RunLocalCallback or SubscriptionHandler::RunLocalCallback functions were used (not necessarily used directly, but via some other function, for example: Node::Request).

Alternatively. there are google::protobuf::DynamicCastMessage and google::protobuf::DownCastMessage functions. Because google::protobuf::DynamicCastMessage function has more sanity checks, it was used in this PR with some additional error logging.

Test it

To test the changes you may install the Google Protocol Buffers v28, write some code that uses RepHandler::RunLocalCallback or SubscriptionHandler::RunLocalCallback (not necessarily directly) with C++ concepts enabled, and try to compile the code.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Rebase-and-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

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This is an automatic backport of pull request #541 done by [Mergify](https://mergify.com).