The access log's response writer had no Unwrap method, so
http.ResponseController stopped at it and a handler's Flush returned
http.ErrNotSupported. It now has one.
With metrics on, adding Unwrap alone is not enough: go-http-metrics'
writer only passes a flush on when the writer inside it has a Flush
method, and it sat inside Logging, so the flush silently did nothing.
Metrics is now registered outside Logging, and the README's middleware
list follows.
A new test flushes through the production router, with the defaults
and with metrics and Sentry on, on a global route and inside an admin
page route group.
Model: opus-5-5
