detect/flowbits: implement prefilter support

Allow for more efficient rules that 'prefilter' on flowbits with 'isset' logic.

This prefilter is enabled by default, which means that if no mpm is present or
no explicit prefilter is used, the flowbits prefilter will be set up for a rule.

flowbits 'isset' prefilter

For rules that have a 'flowbits:isset,<bit>' statement, a "regular" prefilter
facility is created. It means that the rules are removed from the normal
match list(s) and added to a prefilter engine that runs prior to the individual
rule inspection stage.

Implementation: the prefilter is implemented as an RB_TREE of flowbits, with the
rule id's they "enable" stored per tree node. The matching logic is walking the
list of bits set in the flow and looking each of them up in the RB_TREE, adding
the rule ids of each of the matching bits to the list of rule candidates.

The 'isset' prefilter has one important corner case, which is that bits can in
fact be set during the rule evaluation stage. This is different from all other
prefilter engines, that evaluate an immutable state (for the lifetime of the
packet inspection).

flowbits 'set' post-match prefilter

For flowbits 'set' action, special post-match 'prefilter' facilities deal with
this corner case. The high level logic is that these track which 'isset' sigs
depend on them, and add these dependencies to the candidates list when a 'set'
action occurs.

This is implemented in a few steps:

1. flowbits 'set' is flagged
2. when 'set' action occurs the flowbit is added to a "post rule
   match work queue"
3. when the rule evaluation ends, the post-match "prefilter" engine is run
   on each of the flowbits in the "post rule match work queue"
4. these engines ammend the candidates list with the rule id dependencies
   for the flowbit
5. the candidates list is sorted to make sure within the execution for that
   packet the inspection order is maintained

Ticket: #2486.

src/detect-flowbits.h

@@ -1,4 +1,4 @@
-/* Copyright (C) 2007-2010 Open Information Security Foundation
+/* Copyright (C) 2007-2025 Open Information Security Foundation
  *
  * You can copy, redistribute or modify this Program under the terms of
  * the GNU General Public License version 2 as published by the Free
@@ -36,6 +36,9 @@ typedef struct DetectFlowbitsData_ {
     uint32_t idx;
     uint8_t cmd;
     uint8_t or_list_size;
+    /** Flag to trigger post rule match prefilter following a 'set' match. */
+    bool post_rule_match_prefilter; /**< set/toggle command should trigger post-rule-match
+                                       "prefilter" */
     uint32_t *or_list;
 } DetectFlowbitsData;