feat: add `control` and `arrow_telescope` simproc DSL primitives

Add two new `sym_simproc` primitives for use as `pre` simprocs:
- `control` — simplifies control-flow expressions (`if-then-else`,
  `match`, `cond`, `dite`), visiting only conditions and discriminants
- `arrow_telescope` — simplifies arrow telescopes
  (`p₁ → p₂ → ... → q`) without entering binders

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>