enable dispatch load/reload in single binary, add error message with dlerror

[conrade-ctc]

Description

Problem: Load/UnloadDispatchAPI can't but be used multiple time in an application.

Solution: Enable Load/UnloadDispatchAPI by moving data out and allowing controlled reset of static data via UnloadDispatchAPI.

Also: add dlerror() when load fails to get diagnostics on reason for failure (e.g., file not found vs symbols not defined)

Fixes # (issue)

Type of change

Please tick all options which are relevant.

• Bug fix
• New feature
• Requires documentation updates

Testing

Please describe the test(s) that you added and ran to verify your changes.

Checklist

• I have read the contribution guide recently

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.56%. Comparing base (76d0600) to head (86d2002).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #799      +/-   ##
==========================================
+ Coverage   79.46%   79.56%   +0.10%     
==========================================
  Files          11       11              
  Lines        4002     4007       +5     
==========================================
+ Hits         3180     3188       +8     
+ Misses        822      819       -3     

Files with missing lines	Coverage Δ
include/CppInterOp/Dispatch.h	90.62% <100.00%> (+12.84%)	⬆️

Files with missing lines	Coverage Δ
include/CppInterOp/Dispatch.h	90.62% <100.00%> (+12.84%)	⬆️

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[github-actions]

clang-tidy made some suggestions

[conrade-ctc]

@vgvassilev @aaronj0 In getting at least an error message out of dlerror(), the PR reminding me there is no test for Load/Unload, so I also updated that mechanism to enable multiple load/unload cycle (just to enable the test, but of course this is also valuable in general)

[github-actions]

clang-tidy made some suggestions

[github-actions]

clang-tidy made some suggestions

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

clang-tidy made some suggestions

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[conrade-ctc]

@vgvassilev, @aaronj0, I backed out the previous impl that pulled the statics out... I didn't realize you were relying on the inline capture of the statics... in the case, the smallest change is to abuse the dlGetProcAddress function to allow it to reset the data itself when nullptrs are sent in... it's a bit awkward to use the magic invocation, otherwise the changes would need to be a bit more detailed, and you may have other plans for how this shapes up.

FYI, I put something in for the windows version of the error output (but just the error code), but the msvc builds aren't perfectly happy... looking at those now.