isl: rename built-ins 8/9/93 to stopwatch_start/_elapsed/_stop

They are start / read / stop of one of 32 per-phase stopwatches, not
flag operations.  123-127 keep timer_* -- that is the mission timer,
five scalars at [phase+304..320], a different clock.

Artefact check: 84 lines changed across 5 files and all 84 pair
exactly with their old-name partners once column padding is
normalised (0 removed lines without an old name, 0 added lines
without a new one).  data/isl-timers.txt reproduces the same
675/675, 11.2 % control, 82/1 and identical histograms, which is
what shows the rename is cosmetic.

Also withdraws a label from the previous commit: sub_8230C398 is NOT
the message pump.  It runs every frame but drains nothing -- a state
machine on [0x828E1F8C] that only allocates, builds strings, looks up
and PUSHES.  And bus+8216 is weak evidence: sub_82254A08 is a generic
map find with ~120 sites, and the key looked up is a pointer, not a
tag.  The open handle is now the ring buffer at bus+4, not bus+8216.

docs/re/structures/isl-mission-timer.md

@@ -145,11 +145,27 @@ no table of subscribed tags to find either.
 ### 🟡 Where the subscriber actually lives — located, not read
 
 The bus object at `[0x828F35DC]` carries a **map at `+8216`**, looked up through
-`sub_82254A08` from **`sub_823001E8`** — whose only caller is `sub_8230C398`, the
-per-frame message pump (itself called from the frame loop `sub_821A6544` with the
-frame `dt`). So dispatch is a **runtime registry keyed by the tag**, and the
-question "does running out of time end the mission" reduces to: *what inserts into
-`bus+8216`, and with which key.* That insert path is not read here.
+`sub_82254A08` from **`sub_823001E8`** — whose only caller is `sub_8230C398`.
+
+🔴 **Correction to my own label from the previous pass.** I called
+`sub_8230C398` "the per-frame message pump". It is *called* every frame (from
+`sub_821A6470` at `0x821A654C` and from the mission loop `sub_821AA1B0` at
+`0x821AA7DC`, both with the frame `dt`), but **it drains nothing**: its whole
+body is a state machine on the counter at `[0x828E1F8C]`, and across 466
+instructions it calls only an allocator (`sub_8230C160`), string building
+(`sub_8217FA08`), a map lookup (`sub_823001E8`) and a *push* (`sub_8225FEA0`).
+It is a boot/loading sequencer that posts messages, not the consumer of them.
+
+Two further cautions the search turned up:
+
+* `sub_82254A08` is a **generic map find** with ~120 call sites image-wide, and
+  `+8216` is a common offset — the pair alone identifies nothing.
+* The key `sub_823001E8` looks up is a **pointer** (`lwz r4, 13780(r11)` stored
+  and passed by address), **not a message tag**. So `bus+8216` may not be the
+  subscriber registry at all.
+
+**So the drain of the queue at `bus+4` is still unlocated**, and with it the
+answer to whether running out of time ends the mission.
 
 ## 🟡 Not settled