Adapt httr::response to httr2::httr2_response

[nealrichardson]

Mocks saved as .R files by httptest are of class "response" from httr. When these are loaded, they need to be adapted to the shape of "httr2_response".

Many tests are currently skipped because of this: they rely on mocks written by httptest. Look for "HTTR2: adapt httr::response to httr2::httr2_response" in comments/skips throughout the code. Once these tests are unskipped, there may be more issues uncovered.