blob/gcsblob: Handle grpc errors on gcsblob

[dpulpeiro]

This PR fixes an issue where errors returned from an underlying gRPC client are incorrectly classified as Unknown.

Previously, when the gRPC client returned a structured error (e.g., Canceled, DeadlineExceeded, etc.), it was being surfaced as a generic Unknown error. This caused a loss of important context and made error handling more difficult.

For example, an error like (code=Unknown): rpc error: code = Canceled desc = context canceled was masking the actual Canceled status returned by gRPC.

Same approach is used in gcppubsubv2

go-cloud/pubsub/gcppubsubv2/gcppubsub.go

Lines 438 to 440 in 781636d

	func (*topic) ErrorCode(err error) gcerrors.ErrorCode {
	return gcerr.GRPCCode(err)
	}

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[vangent]

Thanks!

[dpulpeiro]

Do you know when the next release will be?

[vangent]

No specific timeline, I usually do one every few months. But you should be able to pick up the change independently of it being labeled as a release using pseudo-versions (https://go.dev/ref/mod#pseudo-versions).