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.
⚠️ Please upload report for BASE (main@023f5bd). Learn more about missing BASE report.
✅ All tests successful. No failed tests found.

Additional details and impacted files

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  Coverage        ?   89.94%           
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  Files           ?      397           
  Lines           ?   110656           
  Branches        ?   110656           
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  Hits            ?    99530           
  Misses          ?     7357           
  Partials        ?     3769           

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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 (e138043) with main (023f5bd)}