This PR adds a System F formalization as a `cbv` tactic benchmark. It is
a translation of the Rocq case study from:
*Definitional Proof Irrelevance Made Accessible* by Thiago Felicissimo,
Yann Leray, Loïc Pujet, Nicolas Tabareau, Éric Tanter, Théo Winterhalter
The authors have given permission to use their development.
The benchmark includes:
- A full System F formalization (substitution lemmas, confluence of
λ-calculus, strong normalization)
- A `pow2DoubleEq` benchmark that verifies 2^(n+1) = 2^n + 2^n via
normalization in System F, measuring both `cbv` tactic time and kernel
checking time for n = 0..6
Co-Authored-By: @david-christiansen
Co-authored-by: David Thrane Christiansen <david@davidchristiansen.dk>