chore(gcs-conformance): add test for downloadAsStream retry headers

[bshaffer]

This is for the review of #5637

There was previously no coverage for the changes made to StorageObject::downloadAsStream to ensure the range headers were retried as expected

[bshaffer]

I modified this because a "listener" should not be expected to return a request and arguments. The ability to modify the request/arguments should be optional

[saranshdhingra]

So, we did this change after the conversation about removing the call by ref arguments :)
Do you wanna go back the old route?

[yash30201]

Or do we change the name to something more appropriate thing like modifyRequestFunction()?

[saranshdhingra]

Not really a conversation of this PR, but I'm not too convinced on the name retryListener anyway.
There is a retryFunction already present, and now we're adding a listener?
The difference isn't exactly clear.

[saranshdhingra]

Small confusion about reverting to modifying arguments inside the retryListener. Except for that LGTM.

[saranshdhingra]

I think these changes are all present in #6073 , so closing this.