Improve error handling and automatic reconnection of PubSub streaming message handler

[WhitWaldo]

Description

Improving error handling and automatic reconnection of the PubSub streaming message handler.

This PR supersedes the contribution here by replacing the three independent ContinueWith continuations and their attendant dedupe flags, fault cache and stream-reset coordination with a single Task.WhenAll supervisor that uses plain async/await. This eliminates the entire class of race conditions the original had to patch. Faults surface through the IDaprSubscription. This uses a completion task instead of a cache-and-rethrow-on-next-subscribe model, so callers who never retry can still observe errors. It also wraps multiple exceptions in an AggregateException, resets hasInitialized in finally so re-subscription works after any termination, and adds an ObjectDisposedException guard.

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Please reference the issue this PR will close: #[issue number]

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation: .NET SDK: Reflect updated PubSub message handler for streaming subscriptions docs#5287

[codecov]

Codecov Report

❌ Patch coverage is 86.81319% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.77%. Comparing base (7469c15) to head (7285c59).

Files with missing lines	Patch %	Lines
...aging/PublishSubscribe/PublishSubscribeReceiver.cs	86.81%	8 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1888      +/-   ##
==========================================
+ Coverage   62.73%   62.77%   +0.04%     
==========================================
  Files         338      338              
  Lines        9883     9913      +30     
  Branches     1157     1165       +8     
==========================================
+ Hits         6200     6223      +23     
- Misses       3363     3367       +4     
- Partials      320      323       +3     

Flag	Coverage Δ
net10.0	62.73% <86.81%> (+0.04%)	⬆️

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