MINOR: cache: Use the filter helpers for cache checks and post-check

MINOR: cache: Use the filter helpers for cache checks and post-check

Rework cache_store_check() to walk the filter configurations with
flt_foreach_conf() in response order instead of iterating the legacy
filter_configs directly. This lets the ordering checks work with the
filter instances, and the legacy checks are skipped in instance mode
since they are handled by the instance parsers.

While here, also accept the decompression filters in the implicit cache
declaration, and reject a response decompression filter placed after the
cache, mirroring the existing compression check.

Same conversion for post_check_cache(), which now references the cache in
matching cache filter configurations through flt_foreach_conf().