Replace meta-rule full-rescan retry with a dependency-driven work queue

[bigio]

do_meta_tests() restarted its entire foreach over meta_check_ready (or meta_pending when finishing) via "goto RULE" every time any meta resolved, re-checking the dependency list of every still-pending meta each time, even ones unaffected by what just resolved. Replace it with an explicit work queue seeded the same way, where resolving a meta pushes only the specific metas listed in its meta_deprules reverse-map (the same map PerMsgStatus::rule_ready() already uses) instead of rescanning everything.

[fkoyer]

Looks good to me except you should either seed the hash with truthy values:

my %queued; @queued{@queue} = (1) x @queue;

or check for existence:

next if exists $queued{$deprule};