perf: speed up bv_decide reflection using Lean.RArray

[hargoniX]

This PR uses Lean.RArray in bv_decide's reflection proofs. Giving speedups on problems with lots of variables.

Implement like #6068, speedup:

# before
λ hyperfine "lean +nightly-2024-12-02 tests/lean/run/bv_reflection_stress.lean"
Benchmark 1: lean +nightly-2024-12-02 tests/lean/run/bv_reflection_stress.lean
  Time (mean ± σ):      1.939 s ±  0.007 s    [User: 1.549 s, System: 0.104 s]
  Range (min … max):    1.928 s …  1.947 s    10 runs
# after
λ hyperfine "lean tests/lean/run/bv_reflection_stress.lean"                                                                                                                                                                                                                        
Benchmark 1: lean tests/lean/run/bv_reflection_stress.lean
  Time (mean ± σ):      1.409 s ±  0.006 s    [User: 1.058 s, System: 0.073 s]
  Range (min … max):    1.401 s …  1.419 s    10 runs

[leanprover-community-bot]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 0b8f50f78d9bb94c5034a5044e662b0b8e37e7ca --onto 3c5e612dc54733cd707becb929457d2f9d8ca6fd. (2024-12-02 16:00:26)