chore: add constant folding benchmarks

[aborgna-q]

Constant folding is currently the part of both the Normalize pass and QSystemLLVMPass.

This PR adds benchmarks for two pathological cases:

• Hugrs with multiple defined functions.
• Hugrs containing tuple wires with many variants.

We'll add some perf fixes on top of these. Having a separate PR lets codspeed print the actual improvements.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.59%. Comparing base (eab787d) to head (ce9846d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1861   +/-   ##
=======================================
  Coverage   86.59%   86.59%           
=======================================
  Files         202      202           
  Lines       32692    32692           
  Branches    31206    31206           
=======================================
  Hits        28310    28310           
  Misses       3097     3097           
  Partials     1285     1285           

Flag	Coverage Δ
python	91.64% <ø> (ø)
qis-compiler	73.60% <ø> (ø)
rust	86.35% <ø> (ø)

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