Add proto.Message roundtrip tests for JSON/YAML output

[apstndb]

Summary

• Add proto_roundtrip_test.go exercising *sppb.ResultSet and submessages (ResultSetMetadata, ResultSetStats) through the production jq output pipeline.
• Verify protojson map roundtrip (TestResultSetProtoJSONRoundtrip) and full encode/decode roundtrip for both --format=json and --format=yaml (TestResultSet*ProtoRoundtrip).
• Reuse synthetic CSV/YAML fixtures and frozen PROFILE JSON fixtures (testdata/profile/*.json).

Test plan

• go test ./...
• go test -run 'TestResultSet.*ProtoRoundtrip|TestResultSetProtoJSONRoundtrip' -v .

Made with Cursor

[gemini-code-assist]

Code Review

This pull request introduces a new test file proto_roundtrip_test.go to verify the roundtrip serialization and deserialization of Spanner ResultSet proto messages to and from JSON and YAML formats. The review feedback suggests improving error handling in decodeFormatToMap by returning an explicit error for unsupported formats instead of silently returning nil, nil, which also requires importing the fmt package.

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[gemini-code-assist]

Add the "fmt" package to the imports so it can be used to return formatted errors for unsupported formats in decodeFormatToMap.

Suggested change

	import (
	"bytes"
	"encoding/json"
	"testing"
	import (
	"bytes"
	"encoding/json"
	"fmt"
	"testing"

[gemini-code-assist]

Instead of silently returning nil, nil when an unsupported format is provided, return an explicit error. This prevents potential nil pointer dereferences or confusing failures downstream in assertProtoFormatRoundtrip.

Suggested change

	default:
	return nil, nil
	}
	default:
	return nil, fmt.Errorf("unsupported format: %s", format)
	}

[apstndb]

Closing: roundtrip tests are redundant with existing YAML goldens and the protojson→jq pipeline; not required for the goccy migration.