Refresh the default actor state tracker in place after a reentrant save

[CasperGN]

Based on #1227. Merge it after that. Until then this diff also shows #1227's commits; this PR's own commits are 83d0e03 and c3b3387.

Description

With actor reentrancy on, each reentrant call gets its own state tracker, while activation, reminders and timers use the default tracker. #1227 fixes stale reads by dropping the default tracker's clean copies of keys a reentrant call saved. The next default read then has to go back to the state store for those keys.

This PR refreshes those entries in place instead, so the next read from activation, a reminder or a timer is served from cache with no state store round trip.

What changed, in dapr/actor/runtime/state_manager.py (_invalidate_default_tracker is renamed to _refresh_default_tracker):

• After a reentrant tracker saves, each saved key that the default tracker holds as clean (change kind none) is updated:
  • a remove drops the entry, as in Actors: invalidate the default state tracker after a reentrant save #1227;
  • an add or update replaces the entry with a clean one holding the saved value and ttl.
• Default entries with pending changes (add, update or remove) are left alone, as before.
• The value is stored in the shape a fresh read returns. A new StateProvider.round_trip_state_value serializes the value and deserializes it as object with the provider's own state serializer. No network call is made. For example a tuple (3, 4) is cached as [3, 4], same as a read from the store.
• Two cases fall back to Actors: invalidate the default state tracker after a reentrant save #1227's eviction:
  • a saved None value, because the provider leaves it out of the write, so a fresh read may find nothing;
  • a custom serializer that fails to decode the value. The write has already committed at that point, so save_state no longer raises after a successful save.

Behaviour change: none for callers, other than fewer state store reads after reentrant saves.

This ports dapr/dotnet-sdk#1912. Thanks to @olitomlinson for pointing out the .NET changes on #1227.

Issue reference

Related to dapr/dapr#10532 (reminders reading stale state with reentrancy) and #1227.

Checklist

• Code compiles correctly
• Created/updated tests
• Extended the documentation (not needed; no public API or documented behaviour changes)

Ran: pytest tests/actor (195 passed), ruff check, ruff format --check, mypy (no issues).

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.93%. Comparing base (fb229bc) to head (c3b3387).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1237      +/-   ##
==========================================
+ Coverage   83.89%   83.93%   +0.03%     
==========================================
  Files         123      123              
  Lines       10265    10284      +19     
==========================================
+ Hits         8612     8632      +20     
+ Misses       1653     1652       -1     

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