fix(database): gRPC schema registration removing schema extensions from adapter models

[kon14]

This addresses a bug where incoming gRPC schema registrations would remove a schema's extensions from its adapter model, effectively dropping its extensions until the Database gets restarted and the adapters repopulated with the contents of DeclaredSchema.

To reproduce:

• Start Core
• Debug Database and set an extension in createSchemaFromAdapter() (or similar)
• Notice how any extended schemas coming from DeclaredSchemas list their extensions as expected
• Bring up a module owning an extended schema
• Notice how that same schema is reregistered without any extensions

I'm using a hacky type any cast for the schema object as the schema types are already messed up to the point where it wouldn't be worth attempting to retype this on the spot.
We'll have to clean these up properly.

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other (please describe)

Does this PR introduce a breaking change?

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the main branch
• When resolving a specific issue, it's referenced in the PR's description (e.g. fix #xxx, where "xxx" is the issue number)