[ty] Evaluate reachability of non-definitely-bound to Ambiguous (#19579)

## Summary

closes https://github.com/astral-sh/ty/issues/692

If the expression (or any child expressions) is not definitely bound the
reachability constraint evaluation is determined as ambiguous.

This fixes the infinite cycles panic in the following code:

```py
from typing import Literal

class Toggle:
    def __init__(self: "Toggle"):
        if not self.x:
            self.x: Literal[True] = True
```

Credit of this solution is for David.

## Test Plan

- Added a test case with too many cycle iterations panic.
- Previous tests.

---------

Co-authored-by: David Peter <mail@david-peter.de>

crates/ty_python_semantic/src/place.rs

@@ -135,6 +135,10 @@ impl<'db> Place<'db> {
             Place::Unbound => Place::Unbound,
         }
     }
+
+    pub(crate) const fn is_definitely_bound(&self) -> bool {
+        matches!(self, Place::Type(_, Boundness::Bound))
+    }
 }
 
 impl<'db> From<LookupResult<'db>> for PlaceAndQualifiers<'db> {