Prevent using DefaultTransport

[alanhamlett]

This adds to #395 to make sure NewTransport is used instead of DefaultTransport.

[dron22]

If we use NewClient, as it was adjusted in #409, the client should always have the custom transport set. Thus default transport will never be used in the option functions and the changes here should not have any effect.

@alanhamlett Am I missing something?

[alanhamlett]

Yea, I saw the same thing but client.Transport is nullable and it doesn't hurt to be extra sure.

[dron22]

If we worry, that transport is unintentionally set to nil, we could also worry that transport is unintentionally set to DefaultTransport somewhere. 🤔

But alright, if you prefer double security, then let's do it. We do not need to change the signature of NewTransport to achieve this though. The previous implementation was simpler and using it as-is will make the reasoning about the option functions easier.

[alanhamlett]

The previous implementation was simpler

The one where I used a GetOrCreateTransport function?

[dron22]

I meant the version before the changes in this PR (NewTransport()), which had no input arguments, and simply returned the custom transport. The new name HTTPTransport is also good, I mainly care about the input argument(s).

Reason: Passing the http client as an input argument makes it harder to reason about the function. Instead of just looking at the function signature, you need to read the implementation to be sure about what it is doing. Also the option of passing nil is handled, which adds more complexity.

[gandarez]

Is this PR still relevant?

[alanhamlett]

Is this PR still relevant?

I think so... we want to remove any coding calling http.DefaultTransport.

[dron22]

Referring to my comment above here.