capture stdout from atags and FINALLY re-enable ci because of that

[lun-4]

problem is that from the new test runner protocol (around 0.12 or 0.13? don't remember) the tests started freezing, i hid it and instead ran the test binary directly, manually, as removing --listen=- made the tests work. after debugging it now (due to general zig 0.14 porting) it turns out that the protocol runs on stdin/stdout, and atags tests involve actually invoking the CLI utility code which will write to stdout.

to properly fix this we need to route stdout to somewhere else, done here via an "IOContext" but i may move that to Context.IOContext in the future so that all utilities can use this kind of code

in turn, zig build test can be finally re-enabled on CI without freezing