How to use ProvisioningServiceClient properly?

[MaximTkachenko]

ProvisioningServiceClient implemets IDisposable interface, where ContractApiHttp.Dispose is called. In ContractApiHttp.Dispose internal instances of HttpClient and HttpClientHandler are disposed.
Questions:

• Why isn't IHttpClientFactory used there? As I understand, it's not a good thing to create and then dispose HttpClientHandler on every request; and here is the next question;
• Should I use ProvisioningServiceClient as a singleton? If yes, is it safe to use the same instances of HttpClient and HttpClientHandler within the entire application lifetime?