impl(v3): remove std::future_error hack

[scotthart]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @scotthart, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly cleans up the codebase by removing a complex and conditional workaround for std::future_error construction. The change streamlines the internal error handling mechanism for asynchronous operations, reflecting an update in the project's C++ standard or compiler/library support that now allows for direct use of the standard std::future_error constructor. This results in more straightforward and maintainable code.

Highlights

• Code Simplification: Removed a substantial conditional compilation block that implemented a compatibility hack for std::future_error constructors.
• Direct Error Construction: The code now directly uses the std::future_error(std::future_errc) constructor, simplifying error handling for futures.
• C++ Standard Alignment: Eliminated a workaround previously needed for older C++ standards or specific libc++ versions, indicating an update in the project's baseline C++ requirements or supported library versions.

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[gemini-code-assist]

Code Review

This pull request is a great simplification, removing a platform-specific hack for creating std::future_error objects. By replacing the MakeFutureErrorImpl helper with direct calls to std::future_error(ec), the code becomes more readable and maintainable. The changes are correct under the assumption that all supported toolchains now provide the std::future_error(std::future_errc) constructor. I have one suggestion to further improve exception messages.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.81%. Comparing base (4447f67) to head (703385f).
⚠️ Report is 1 commits behind head on prepare-for-v3.0.0.

Additional details and impacted files

@@                  Coverage Diff                   @@
##           prepare-for-v3.0.0   #15904      +/-   ##
======================================================
- Coverage               92.82%   92.81%   -0.01%     
======================================================
  Files                    2354     2354              
  Lines                  216302   216300       -2     
======================================================
- Hits                   200780   200769      -11     
- Misses                  15522    15531       +9     

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