chore: bring in spicedb and update compilation

[tstirrat15]

Description

This is a part of getting the composable schema package unified in our tooling, which will (eventually) provide a better DX.

Changes

TODO

Testing

Review.

[tstirrat15]

Current TODOs and notes:

• This code depends on chore: make development system filesystem-aware spicedb#2965. It should be run locally against that with go.work, and that PR should also be tested against spicedb-vscode.

• Merge chore: make development system filesystem-aware spicedb#2965 and then go get that SHA to make this reference that code.
• Validation tests are failing. My best guess is that one if not all of the failures have to do with the DirFS() that's being handed to the DevContext in the validate command - it needs to match the dir of the validation file, not the invocation dir.
• Need to check whether validations against just schemas are pointing their warnings at the correct lines (this should be captured in a test, but should also be validated)
• It needs a test of a schema that imports another schema and there's a validation warning/error in that other schema to see whether it points at the correct file and line within that file
• This should be hand-tested against a few things as well - validation files in the example repo, some composable schema stuff, etc.