Add ByteString ToReadOnlySpan()

[fmg-lydonchandra]

Is your feature request related to a problem? Please describe.
Currently to deserialise RabbitMQ Incoming message, we do ByteString.ToArray(), which does memory copy

        var evt = JsonSerializer.Deserialize<T>(message.Message.Bytes.ToArray(), SerializerOptions);

Describe the solution you'd like
Add ByteString ToReadOnlySpan() which will avoid memory copy if ByteString is compact

Describe alternatives you've considered
No alternative so far

Additional context
#7487