Tests for the #[export] macro

[andybalaam]

I thought there was a bug in the #[export] macro so I wrote some tests. It seems to be fine, but the tests are hopefully still useful.

• This PR makes no API changes so needs no changelog entry
• No AI was used to make this PR

[andybalaam]

@poljar is it OK for me to set tests = true in bindings/matrix-sdk-ffi-macros/Cargo.toml? (This PR does that, so I can run the tests.)

[poljar]

@poljar is it OK for me to set tests = true in bindings/matrix-sdk-ffi-macros/Cargo.toml? (This PR does that, so I can run the tests.)

I think you can also just remove that line, yes it's fine.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.88%. Comparing base (4bd5e81) to head (5c57ccf).
⚠️ Report is 12 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6691      +/-   ##
==========================================
- Coverage   89.89%   89.88%   -0.01%     
==========================================
  Files         396      396              
  Lines      110412   110412              
  Branches   110412   110412              
==========================================
- Hits        99258    99249       -9     
- Misses       7370     7380      +10     
+ Partials     3784     3783       -1     

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[codspeed-hq]

Merging this PR will not alter performance

✅ 50 untouched benchmarks

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_{Comparing andybalaam/test-export-macro (5c57ccf) with main (567463d)}