What Does This Do

Avoid an intermittent ReadPendingException in the Jetty 9.0.0 continuation
test handler by parsing URL-encoded forms before suspending the request.

If parsing commits a blocking response, mark the request handled and return
without suspending or dispatching it.

Add a regression test that sends 100 form requests with HTTP connection
retries disabled. It verifies response status and body, one trace per
request, converted-body tags, and async dispatch spans.

Only test code changes; production instrumentation is unchanged.

Motivation

The shared HTTP test client sends Expect: 100-continue for requests with a
body. This asks the server to acknowledge the request before the client
sends the body.

When form parsing happens after a continuation resumes, the body read can
overlap with Jetty 9.0.0's pending connection read and cause
ReadPendingException. Parsing before suspension avoids this timing.

Additional Notes

The regression test retains the Expect: 100-continue handshake while
disabling connection retries, so retries cannot hide request failures.
It runs under both HTTP naming conventions.

NOTE: This is a workaround in the test handler, not a fix to Jetty itself.