feat(stdlib): Test framework improvements

[tibordp]

• Make test module more useful
• Add a span of the defined item to make tests with wrong signature easier to find
• Change fmt thread-local buffer to a stack-allocd one
• Fix name resolution in alumina-doc for absolute paths

[codecov]

Codecov Report

Attention: Patch coverage is 68.96552% with 9 lines in your changes missing coverage. Please review.

Project coverage is 88.63%. Comparing base (2288cde) to head (f77e501).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/alumina-boot/src/ir/mono/intrinsics.rs	67.85%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #114      +/-   ##
==========================================
- Coverage   88.66%   88.63%   -0.04%     
==========================================
  Files          35       35              
  Lines       17090    17119      +29     
==========================================
+ Hits        15153    15173      +20     
- Misses       1937     1946       +9     

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