Add EntityFactoryWithNs

[C88-YQ]

🎉 New feature

Closes #

Summary

This PR adds two new message types for spawning entities with namespace support:

• EntityFactoryWithNs: extends the existing entity factory pattern with an optional ns field using StringMsg, allowing callers to specify or override the namespace when creating an entity.
• EntityFactoryWithNs_V: adds a repeated container message for sending multiple EntityFactoryWithNs requests together.

Backport Policy

• This is safe to backport to the following versions:
  • Jetty
  • Ionic
  • Harmonic
  • Fortress
• This should not be backported
• I am not sure
• Other (fill in yourself)

Checklist

• Signed all commits for DCO
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• 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)
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• All tests passed (See test coverage)
• Updated Bazel files (if adding new files). Created an issue otherwise.
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[azeey]

Any reason for this to be StringMsg instead of string? Would setting it to an empty string not be sufficient? Or are you thinking of a usecase where the namespace in the model is replaced with "" (empty namespace)?

[C88-YQ]

Yes, the main reason is to distinguish between not set and set to an empty string.

If the user does not provide a namespace, I want to keep the existing namespace and avoid applying any override. But if the user explicitly sets it to "", that should be treated as an override that clears the namespace. A plain string would not let us distinguish those two cases, since its default value is also "".