A strict CWA file (`from __future__ import __cwa__`) now distinguishes
nullable from non-nullable types:
- `name: T?` resolves to `Ptr(T)` and records the slot as nullable
(a per-function slot table, like the released-slot table).
- assigning `None` to a non-nullable declaration, plain assignment,
annotated attribute/subscript target or return type fails fast with a
TypeError; `T?` accepts it.
- class-name extraction unwraps `NullableT[...]`, so field lookup,
method dispatch and `AnnotClassName` still see the class.
Non-strict files keep the previous behavior (`T* = None` is accepted);
`T?` also parses there as `Ptr(T)`, it just carries no enforcement.
Probe: strict `p: A? = None` / `p = new heap hlife A()` / `p = None`
works and null comparisons run; `p: A = None`, `p: A* = None`,
`q = None` on a non-nullable variable and `-> T*` + `return None` all
fail fast; `-> A?` and field `next: A?` work; the same `T* = None`
still compiles outside strict mode. Self-host 110/110; ListTest,
GenericTest3, PtrOpProbe, HashLibTest, NewTest, NewLifetimeTest,
StructTest and EscapeOkTest pass.
TermiNexus
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