refactor!: Rename wait_for_finish to wait in Actor.start

[vdusek]

Description

• Rename the wait_for_finish: int | None argument of Actor.start() to wait: timedelta | None, unifying it with Actor.call() and Actor.call_task(), which already use wait: timedelta for the same concept.
• The argument is keyword-only, so old call sites fail with a TypeError instead of silently misbehaving. Behavior is unchanged, the server-side cap of 300 seconds still applies.
• Fix the wait docstrings of Actor.call() and Actor.call_task(), which still said "maximum number of seconds" for a timedelta argument.
• Document the rename in the v4 upgrading guide.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.88%. Comparing base (a87e8d1) to head (a1e295b).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #962      +/-   ##
==========================================
- Coverage   90.00%   89.88%   -0.13%     
==========================================
  Files          49       49              
  Lines        3053     3085      +32     
==========================================
+ Hits         2748     2773      +25     
- Misses        305      312       +7     

Flag	Coverage Δ
e2e	35.98% <ø> (+0.31%)	⬆️
integration	56.95% <ø> (+0.09%)	⬆️
unit	78.70% <ø> (-0.01%)	⬇️

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