TypedPython: an impure function calling a compiled function with a class parameter crashes cgen instead of compiling or skipping #275

Repro: fresh(a, n) does c = Cell(None, None); seta(c, a) where seta(c: Cell, v) is compiled. frontend and verify accept fresh (impure, may_deopt=False, verify.py:1011 uses exact_of: c is new-only Cell), but cgen _can_deopt (cgen.py:393, also :822) treats any non-redo Call to a callee with a Param.cls parameter as deopting, so the whole module fails with CGenError.

To decide: is the callee's entry class guard really unfailing here on 3.15t (another thread can modify the class between New and the call), or must verify agree with cgen and skip fresh with a reason.

Done when: the module never crashes in cgen; fresh either compiles with a proven-sound call or is skipped with a reason; a test in the pipeline tests covers it.