Replace log using log/slog

[jiayx]

Replace log using log/slog

[google-cla[bot]]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[jiayx]

56

[marten-seemann]

This PR is missing the point of of slog/log. There no value in just replacing all log calls with slog.

The value comes from users being able to provide their own loggers.