Run bg-transform callbacks while wait/track-blocked

Background transform results are unrelated to the block; dropping them
would silently lose completed work. Applies both the dedicated
bg-transform-* setters and actions parsed from generic bg-transform
output (inBgCallback). Searches initiated by a bg result are not
waited for.

man/man1/fzf.1

@@ -2322,6 +2322,12 @@ While waiting, user input is ignored, except for keys bound to \fBabort\fR or
 default), which cancel the wait and discard the pending actions instead of
 performing their usual role.
 
+Asynchronous \fBbg\-transform\-*\fR actions are not affected; their results are
+applied as soon as they arrive, even while waiting. Note that \fBwait\fR only
+considers searches already in progress or triggered by the preceding actions in
+the same binding; a search initiated later by a \fBbg\-transform\fR result is
+not waited for.
+
 If the search takes long enough, fzf indicates that it is waiting by dimming the
 input, hiding the cursor, and showing \fB(..)\fR on the info line. This visual
 feedback is debounced so that quick searches do not cause flickering.