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 Tables.jl-compatible object, which requires manual conversion to DataFrame for analysis

Rationale:

• JET causes terrible compatibility conflicts
• Chairmarks is not MIT-licensed
• DataFrames is a heavy dep

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.21%. Comparing base (8d33550) to head (4981006).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #958   +/-   ##
=======================================
  Coverage   98.20%   98.21%           
=======================================
  Files         133      135    +2     
  Lines        7983     8002   +19     
=======================================
+ Hits         7840     7859   +19     
  Misses        143      143           

Flag	Coverage Δ
DI	98.97% <ø> (ø)
DIT	96.22% <100.00%> (+0.03%)	⬆️

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