[ty] Avoid caching trivial member lookups (#25661)
## Summary
`member_lookup_with_policy` currently creates and retains a Salsa query
even when the result is known before attribute lookup: for `__class__`,
and for dynamic, divergent, and `Never` types.
This change handles those cases before entering the tracked query.
Materialized divergent fallbacks and the existing `__class__` ordering
are preserved; all other lookups continue through the unchanged tracked
implementation.
