firestore: option.WithTelemetryDisabled() does not disable telemetry

we disable telemetry with this on New
```go
firestoreClient, err := firestore.NewClient(ctx, "...", option.WithTelemetryDisabled())
```

now, we still see that telemetry is sent. here span it generates for accessing document in firestore.

go.mod
```
go 1.25.0

require (
cloud.google.com/go v0.123.0
cloud.google.com/go/bigquery v1.71.0
cloud.google.com/go/firestore v1.18.0
cloud.google.com/go/pubsub/v2 v2.2.0
cloud.google.com/go/storage v1.57.0

...

github.com/redis/go-redis/extra/redisotel/v9 v9.14.0
github.com/redis/go-redis/v9 v9.15.1
github.com/riandyrn/otelchi v0.12.2
go.opentelemetry.io/contrib/detectors/gcp v1.38.0
go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.63.0
go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.63.0
go.opentelemetry.io/contrib/instrumentation/runtime v0.63.0
go.opentelemetry.io/otel v1.38.0
go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.38.0
go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.38.0
go.opentelemetry.io/otel/metric v1.38.0
go.opentelemetry.io/otel/sdk v1.38.0
go.opentelemetry.io/otel/sdk/metric v1.38.0
go.opentelemetry.io/otel/trace v1.38.0
golang.org/x/crypto v0.42.0
golang.org/x/sync v0.17.0
google.golang.org/api v0.251.0
google.golang.org/genai v1.28.0
google.golang.org/grpc v1.75.1
google.golang.org/protobuf v1.36.10
```