[ty] Protocols: Fixpoint iteration for fully-static check (#17880)

## Summary

A recursive protocol like the following would previously lead to stack
overflows when attempting to create the union type for the `P | None`
member, because `UnionBuilder` checks if element types are fully static,
and the fully-static check on `P` would in turn list all members and
check whether all of them were fully static, leading to a cycle.

```py
from __future__ import annotations

from typing import Protocol

class P(Protocol):
    parent: P | None
```

Here, we make the fully-static check on protocols a salsa query and add
fixpoint iteration, starting with `true` as the initial value (assume
that the recursive protocol is fully-static). If the recursive protocol
has any non-fully-static members, we still return `false` when
re-executing the query (see newly added tests).

closes #17861

## Test Plan

Added regression test

crates/ty_python_semantic/resources/mdtest/protocols.md

@@ -1558,7 +1558,43 @@ def two(some_list: list, some_tuple: tuple[int, str], some_sized: Sized):
     c: Sized = some_sized
 ```
 
-## Regression test: narrowing with self-referential protocols
+## Recursive protocols
+
+### Properties
+
+```py
+from __future__ import annotations
+
+from typing import Protocol, Any
+from ty_extensions import is_fully_static, static_assert, is_assignable_to, is_subtype_of, is_equivalent_to
+
+class RecursiveFullyStatic(Protocol):
+    parent: RecursiveFullyStatic | None
+    x: int
+
+class RecursiveNonFullyStatic(Protocol):
+    parent: RecursiveNonFullyStatic | None
+    x: Any
+
+static_assert(is_fully_static(RecursiveFullyStatic))
+static_assert(not is_fully_static(RecursiveNonFullyStatic))
+
+static_assert(not is_subtype_of(RecursiveFullyStatic, RecursiveNonFullyStatic))
+static_assert(not is_subtype_of(RecursiveNonFullyStatic, RecursiveFullyStatic))
+
+# TODO: currently leads to a stack overflow
+# static_assert(is_assignable_to(RecursiveFullyStatic, RecursiveNonFullyStatic))
+# static_assert(is_assignable_to(RecursiveNonFullyStatic, RecursiveFullyStatic))
+
+class AlsoRecursiveFullyStatic(Protocol):
+    parent: AlsoRecursiveFullyStatic | None
+    x: int
+
+# TODO: currently leads to a stack overflow
+# static_assert(is_equivalent_to(AlsoRecursiveFullyStatic, RecursiveFullyStatic))
+```
+
+### Regression test: narrowing with self-referential protocols
 
 This snippet caused us to panic on an early version of the implementation for protocols.