REGTESTS: filters: Record Lua callback waits across backend EOF

REGTESTS: filters: Record Lua callback waits across backend EOF

While exercising callback resumption, a complete chunked response could
be lost when the backend closed while Lua filters were waiting. The
related EOF race was also observed with legacy filters on the pre-series
build; it is independent of instance parsing and sequencing.

Keep an EOF reproducer separate from the passing resumption test, which
uses a barrier to hold the backend open. Exercise legacy and instance
chains and keep-alive reuse, and mark the test broken until the EOF race
is fixed. Allow the shared probes to configure their wait delay.