Teach the trailing-log gate to see command-substitution call sites

Found while fixing count_log_pattern: the gate reported that function clean
even though it ends in echo and both callers consume its status. Its call-site
patterns only matched direct forms -- if fn, while fn, fn ||, fn && -- so a
status consumed through command substitution was invisible, because the line
begins with the variable rather than the function name.

That is not an exotic form. It is how a shell function returns a value, and it
is precisely the shape of the swallowed-failure family this gate exists to
catch, so the gate was blind to a large part of its own stated class.

Three patterns added for the assignment, if-guarded and test-expression forms.
The extension finds four real instances, all value-returning helpers whose
trailing echo made their exit status unconditionally zero, and each now carries
an explicit return 0. Also corrects the finding message, which described the
trailing command as a log call; for these it is the return mechanism, and the
hazard is that it fixes the status either way.

Validated by breaking what it guards: a probe reintroducing the defect shape
behind a command substitution is reported and exits 1, where before the
extension it would have passed.

testing/static/scripts/bench-multirun.sh

@@ -120,6 +120,7 @@ ping_path() {
         return
     fi
     echo "${rtt//\// } ${loss:-N/A}"
+    return 0
 }
 
 # ── Path definitions ───────────────────────────────────────────────────────

testing/static/scripts/generate-configs.sh

@@ -74,6 +74,7 @@ docker_host_name() {
     local host
     host=$(get_node_attr "$topology_file" "$node_id" "docker_host")
     echo "${host:-node-$node_id}"
+    return 0
 }
 
 # Get peers list from topology
@@ -118,6 +119,7 @@ get_default_transport() {
     local topology_file="$1"
     local transport=$(grep "^default_transport:" "$topology_file" | head -1 | sed 's/.*: *\([a-z]*\).*/\1/')
     echo "${transport:-udp}"
+    return 0
 }
 
 # Get the port for a given transport type

testing/static/scripts/netem.sh

@@ -159,6 +159,7 @@ build_netem_params() {
     fi
 
     echo "$params"
+    return 0
 }
 
 # Check if a container is running