fix: `runner.CapturePrintOutput` setting never read (#9104)

Setting `field-writes-are-uses: false` in the `unused` linter revealed
quite a few locations where we either have dead code, or code that
doesn't do what we intended. This fixes one of those issues.

While the runner API exposes a `CapturePrintOutput` this value was never
read, but would be hardcoded to `true` for tests and `false` for
benchmarks. This fixes that so that the setting is honored by the test
runner (but still defaulting to `true) when running regular tests. The
value remains hardcoded to `false` for benchmarks as it's unlikely to
help anyone getting thousands of lines printed running those.

Also a few improvements in related code.

Signed-off-by: Anders Eknert <anders.eknert@apple.com>