Use ArtifactManager and ChassisManager to replace EntityManager.

[Chounoki]

No description provided.

[gemini-code-assist]

Code Review

This pull request refactors the Bootz server to replace the EntityManager with separate ArtifactManager and ChassisManager interfaces, introducing an in-memory chassismanager implementation. Additionally, the Sign function in the signature package has been updated to return raw bytes instead of a base64-encoded string.

Critical feedback includes a compilation failure in server/emulator/main.go due to an outdated call to NewServer. Other recommendations focus on preventing nil pointer dereferences by adding nil checks for configurations and mandatory dependencies, handling potential whitespace in certificate serial numbers, and extracting duplicated code for retrieving the server trust anchor certificate into a helper method.

[Chounoki]

Thanks for reviewing!