This removes the need to spin up a web server for each test, instead,
mocking the necessary methods to do everything in line. This will make
the tests much more resilient, and with the remaining WriterGate changes
expected in zig 0.16, I suspect the mocking will be unnecessary in the
next release.
There are several test issues that remain:
* Two skipped tests in signature verification. This is the most
concerning of the remaining issues
* Serialization of [][]const u8 was probably broken in zig 0.14.1, but
the new version has surfaced this issue. Warning messages are being
sent, and this needs to be tracked down
* One of the tests is failing as S3 storage tier extra header is not
being offered. I'm not sure what in the upgrade might have changed
this behavior, but this needs to be investigated
