fix documentation for ExecuteOutcomeAsync (#2680)

[carvex21]

Pull Request

The issue or feature being addressed

Fix the Documentation that has incorrect examples for ExecuteOutcomeAsync #2680

Details on the issue fix or feature implementation

• Markdown documentation fixes:

1. Migration Guide (migration-v8.md)
   Replaced example that passed a throwing callback with the safe pattern: wrapping the MethodAsync call in try/catch and returning either Outcome.FromResult(...) or Outcome.FromException(...).

2. Fallback Strategy (fallback.md)
   Updated the “✅ DO” snippet to wrap user code in try/catch and properly return Outcome, enabling exception remapping logic without throwing from the callback.

3. Circuit Breaker Strategy (circuit-breaker.md)
   Rewrote the “✅ DO” example to include exception capture via Outcome, and updated post-execution logic to correctly handle both BrokenCircuitException and other errors.

• XML documentation updates. Strengthened the section on ExecuteOutcomeAsync<TResult, TState> to emphasize that the callback must not throw; users must wrap their code and return an Outcome. This clarifies the contract and prevents accidental misuse that relies on internal implementation details. Files affected:

1. ResiliencePipeline.AsyncT.cs
2. ResiliencePipelineT.Async.cs

• Snippet corrections:

1. Migration.Execute.cs (snippets used in docs)
   Updated the V8 example (SafeExecute_V8) to use the correct, safe callback pattern: wrapping in try/catch and returning an Outcome. This ensures consistency across sample code and real documentation.

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[carvex21]

@dotnet-policy-service agree

[martincostello]

The snippets don't compile - please check that they build before committing changes to them.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.12%. Comparing base (651508b) to head (950a4fd).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2710   +/-   ##
=======================================
  Coverage   96.12%   96.12%           
=======================================
  Files         309      309           
  Lines        7118     7118           
  Branches     1008     1008           
=======================================
  Hits         6842     6842           
  Misses        222      222           
  Partials       54       54           

Flag	Coverage Δ
linux	96.12% <ø> (ø)
macos	96.12% <ø> (ø)
windows	96.11% <ø> (ø)

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[martincostello]

Thanks for the contribution.