refactor(sdk): Some error refactoring

[zecakeh]

The 2 first commits are a bit of cleanup. The last one makes RumaApiError a type alias of UiaaResponse because they are identical except for variant names so it might be more controversial.

• I've documented the public API Changes in the appropriate CHANGELOG.md files.
• This PR was made with the help of AI.

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.93%. Comparing base (c253114) to head (c737a7f).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/matrix-sdk/src/encryption/mod.rs	50.00%	0 Missing and 1 partial ⚠️
...rates/matrix-sdk/src/widget/machine/from_widget.rs	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6574   +/-   ##
=======================================
  Coverage   89.92%   89.93%           
=======================================
  Files         381      381           
  Lines      107718   107703   -15     
  Branches   107718   107703   -15     
=======================================
- Hits        96870    96865    -5     
+ Misses       7173     7164    -9     
+ Partials     3675     3674    -1     

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[codspeed-hq]

Merging this PR will not alter performance

✅ 47 untouched benchmarks
⏩ 3 skipped benchmarks¹

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_{Comparing zecakeh:refactor-error (c5ad7b7) with main (2a8d75e)}

Footnotes

1. 3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[stefanceriu]

Looks good to me, thanks Kevin! Please change the.. chagelog and then I'll merge it 🙂