REGTESTS: filters: Exercise Lua probes around mixed built-in filters

REGTESTS: filters: Exercise Lua probes around mixed built-in filters

Inherit a chain combining Lua, trace, cache, compression and bandwidth
filters from named defaults. Position Lua probes before and after request
and response compression and verify the encoding each probe observes.
Activate both bandwidth directions and validate the forwarded bodies.

Populate the cache with an uncompressed body, replay it to a client not
accepting gzip and verify that the response probes still run on a hit.
Override compression and response bandwidth state on a sibling backend
without changing the enabled sibling or the inherited Lua probes.