feat: unmarshal grpc-status-details-bin trailer into error details

[yordis]

What?

Read the grpc-status-details-bin trailer from gRPC error responses and expose its structured details in response.error.details in k6 test scripts.

Also fixes marshaling of standard Google protobuf types in error responses by using Resolver: nil instead of the per-connection user-defined type registry.

Why?

gRPC servers use the grpc-status-details-bin trailer as the standard mechanism to attach rich structured error information — things like ErrorInfo (reason, domain, metadata), BadRequest field violations, RetryInfo, etc. Previously k6 ignored this trailer entirely, always returning an empty details array even when the server sent structured errors.

Two issues were preventing this from working:

1. The trailer was never read — response.error.details was always empty regardless of what the server sent.
2. Even if the trailer had been read, the error was marshaled using Resolver: c.types, which only knows about user-defined protobuf types loaded via client.load(). Standard Google types like google.rpc.ErrorInfo are not in that registry, so they would marshal to empty objects. Using Resolver: nil falls back to the global protobuf registry which resolves them correctly.

Checklist

• I have performed a self-review of my code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have added tests for my changes.
• I have run linter and tests locally (make check) and all pass.

Checklist: Documentation (only for k6 maintainers and if relevant)

Please do not merge this PR until the following items are filled out.

• I have added the correct milestone and labels to the PR.
• I have updated the release notes: link
• I have updated or added an issue to the k6-documentation: grafana/k6-docs#NUMBER if applicable
• I have updated or added an issue to the TypeScript definitions: grafana/k6-DefinitelyTyped#NUMBER if applicable

Related PR(s)/Issue(s)

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