Preview SDK generation from legacy public proto

[hectorcast-db]

Summary

Preview-only sync of the current Universe databricks-sdk-py subtree with the generated databricks/sdk surface replaced by the legacy public-proto generator output. This draft is for inspecting the migration diff and is not intended to merge.

Why

The Python SDK currently generates from OpenAPI. This PR makes the in-progress public-proto migration visible in the public repository so the generated output can be reviewed directly.

What changed

Interface changes

The generated SDK surface now comes from the legacy public-proto descriptor. Overlapping APIs match the OpenAPI output semantically. Synthesized permissions APIs and ServingEndpointsDataPlane are intentionally absent here; they are expected to remain handwritten mixins.

Behavioral changes

Preview only. Do not merge.

Internal changes

The committed SDK subtree and OpenAPI-generated docs come from the normal Universe-to-OSS sync. Only the generated Python SDK surface was replaced with the legacy public-proto render.

How is this tested?

• Built both the OpenAPI and legacy public-proto Python SDK renders with Bazel.
• Ran the focused public-proto transformation and lint tests.
• Compared generated Python ASTs: zero class, field, method, or annotation mismatches across overlapping APIs. The remaining old-only surface is the expected permissions and dataplane mixin work.
• git diff --check passes.

[github-actions]

If integration tests don't run automatically, an authorized user can run them manually by following the instructions below:

Trigger:
go/deco-tests-run/sdk-py

Inputs:

• PR number: 1563
• Commit SHA: bc391eabd6308f631747c17ddcddf93520daadcc

Checks will be approved automatically on success.