fix!: turn Chairmarks and JET into weakdeps

[gdalle]

Warning

Breaking changes:

• Move benchmarking and type stability testing to package extensions: they now require Chairmarks / JET to be loaded manually
• Change output type of benchmarking to a table instead of a DataFrame

Rationale:

• JET causes terrible compatibility conflicts
• Chairmarks is not MIT-licensed

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.22%. Comparing base (8d33550) to head (80ec41d).

Files with missing lines	Patch %	Lines
...ifferentiationInterfaceTest/src/tests/benchmark.jl	44.44%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #958      +/-   ##
==========================================
- Coverage   98.20%   97.22%   -0.99%     
==========================================
  Files         133      131       -2     
  Lines        7983     7974       -9     
==========================================
- Hits         7840     7753      -87     
- Misses        143      221      +78     

Flag	Coverage Δ
DI	97.89% <ø> (-1.09%)	⬇️
DIT	95.49% <80.00%> (-0.71%)	⬇️

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