fix(transport): use ds.GetUniverseDomain() instead of raw ds.UniverseDomain field

[yaroshevichg]

Summary

Fixes an issue where GOOGLE_CLOUD_UNIVERSE_DOMAIN environment variable settings are ignored when dialing gRPC or HTTP transports unless option.WithUniverseDomain is explicitly passed in code.

Root Cause

DialSettings.GetUniverseDomain() resolves the effective universe domain by checking ds.UniverseDomain, falling back to GOOGLE_CLOUD_UNIVERSE_DOMAIN, and defaulting to "googleapis.com".

However, transport/grpc/dial.go and transport/http/dial.go populate UniverseDomain using the raw struct field ds.UniverseDomain. When a client relies on GOOGLE_CLOUD_UNIVERSE_DOMAIN from the environment without explicitly calling option.WithUniverseDomain(...), ds.UniverseDomain is empty (""), causing the transport layer to ignore the environment variable.

Solution

Use ds.GetUniverseDomain() when passing UniverseDomain in transport/grpc/dial.go and transport/http/dial.go.