fix(events): open the platform websocket only once per context

[vdusek]

ApifyEventManager ignored the re-entrancy contract of Crawlee's EventManager, which tracks active contexts with _active_ref_count. BasicCrawler._run_crawler always enters the global event manager, and Actor.init registers the ApifyEventManager as exactly that and has already entered it — so on the platform every crawler run re-entered it and opened a second websocket.

Measured on master, with a local events server and a BasicCrawler.run() inside an entered ApifyEventManager:

• Two connections stay open for as long as the run lasts, so every platform event arrives twice. One Migrating became two Migrating listener calls and two PersistState(is_migrating=True) — state persisted twice per migration. The extra connection also counts against the platform limit of 10 per run.
• The crawler's exit tears down that newer connection, which leaves __aexit__ bookkeeping pointing at an already-closed one. The Actor's own connection and its message-processing task therefore survive Actor.exit(), re-breaking the iterator shutdown from fix: close the platform events websocket iterator on shutdown #1077.

The websocket is now owned by the outermost context only, mirroring LocalEventManager. On top of that:

• The shutdown moved into _teardown_platform_websocket() and the parent context is left in a finally, so a failed shutdown can no longer keep the manager active for good — which would mean never emitting PersistState again.
• Task, connection and future are reset on exit, so the context can be entered again.
• A cancelled entry cleans up as well. Without it, a later entry mistook itself for a nested context and silently returned a manager that received no platform events at all.
• The error that prevented the first connection is raised as the __cause__ of the RuntimeError, not only logged.
• Actor.reboot() reads _listeners_to_wrappers with get, so the lookup no longer inserts entries for events nobody listens to.

Adopts the patterns from apify/crawlee-python#2100 (Crawlee 1.9.1).

✍️ Drafted by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.23%. Comparing base (7d23ecd) to head (e3518a7).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1082      +/-   ##
==========================================
+ Coverage   92.20%   92.23%   +0.03%     
==========================================
  Files          51       51              
  Lines        3231     3247      +16     
==========================================
+ Hits         2979     2995      +16     
  Misses        252      252              

Flag	Coverage Δ
e2e	35.20% <2.63%> (-0.15%)	⬇️
integration	56.63% <2.63%> (-0.25%)	⬇️
unit	84.50% <100.00%> (+0.07%)	⬆️

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[Mantisus]

LGTM