M12: XFA script time limits start when the engine is ready (#1081)

* M12: XFA script time limits start when the engine is ready

An XFA script's wall-clock limit (1 s for scripts that run unasked, such
as initialize and calculate) also counted the engine's start-up: the
script thread, a new boa Context, and for the first script in a process
the engine's own one-time set-up (~60-170 ms when idle, shared by every
script starting at the same moment). On a busy machine a trivial
initialize script could pass 1 s, be abandoned, and so turn all of the
form's scripts off, with the error only in the JavaScript console.

That made two ui-egui xfa.rs tests flaky
(xfa_buttons_run_their_scripts_in_the_app,
messages_from_scripts_run_on_open_show_right_away): under full CPU load
25 of 40 runs of the test binary failed, and none of 40 with this
change.

- run_within: the script calls `started` once the engine is ready, and
  the time limit runs from then. Start-up has a cap of its own (10 s),
  so a caller still never waits forever.
- run_here: a once-per-process warm-up script takes the engine's first
  use, so the first form script's timed part drops from ~52 ms to under
  ~11 ms.
- FormCalc (no engine to start) signals at once, as before.
- Tests: a slow start doesn't abandon a script; the script's own time,
  and start-up, are still capped. The UI tests print the script console
  when they fail.

Runaway scripts are still abandoned at the same limits
(runaway_xfa_calculations_at_open_end_quickly_with_a_report).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Add arcanii to the contributor names

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>

contributors/people.toml

@@ -74,3 +74,8 @@ sync_github_name = true
 
 [people.jay-tau]
 sync_github_name = true
+
+[people.arcanii]
+real_name = "Bryan Mark"
+display_name = "Arcanii"
+sync_github_name = false