fix(sr-normalize): reference inlined deps by their local name

[birdayz]

What

Fix cross-package dependency references in protoc-gen-go-sr-normalize. A message whose field type lives in a different proto package produced a schema with a dangling type reference that Schema Registry rejects. Same-package schemas are byte-identical to before.

Why

The plugin builds a single self-contained schema by inlining every non-WKT transitive dependency as a top-level type in the target's package. The reference-naming logic stripped only the package prefix that the referred type shared with the referring message. That is fine while everything sits in one package, but wrong across packages.

Concrete case that motivated this: redpanda.api.adp.v1alpha1.LLMProviderType referenced from a message in redpanda.adp.v1alpha1. The shared prefix is just redpanda., so the reference came out as api.adp.v1alpha1.LLMProviderType while the enum was inlined top-level as LLMProviderType. Dangling reference, schema rejected. The workaround so far was to duplicate the enum into the referring package, which is exactly what this makes unnecessary.

Implementation details

Reference each type by its path within its own file: strip the type's own package prefix, not the prefix it happens to share with the referrer. A top-level type resolves to its bare name; a nested type to Parent.Nested, matching how the generator renders inlined types (flattened into one package, nesting preserved). Well-known google/protobuf/* types are kept as imports, so they retain their full name.

The change is contained to the naming path: relativeName (shared-prefix stripping) is replaced by localTypeName (own-package stripping) behind schemaTypeName, which also handles the well-known case.

New example proves the cross-package path end to end: example.other.v1.ProviderType (a separate package) referenced by an annotated example.v1.Event. TestSchemaRegistry_EventRoundTrip registers the generated schema against a real Schema Registry and round-trips a message. A unit test pins the naming logic directly.

The order.pb.go / product.pb.go diffs are a regeneration, not a functional change. Their checked-in go_package had been renamed textually from protoc-gen-go-sr to protoc-gen-go-sr-normalize without regenerating, which left the descriptor's varint length prefix stale (87 vs the actual 97 bytes) and panics at package init. Regenerating corrects the descriptor; the .sr.pb.go outputs are unchanged.

References

Discovered while moving proto packages around, where the cross-package enum reference forced a duplicate enum definition.

[secpanda]

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