[anneal] Spec generation uses unqualified type names for imported Rust types

[nnunley]

When a Rust function uses a type via use import (e.g., use std::sync::atomic::Ordering), Anneal's spec generator derives the Lean type name from the syn AST, which only contains the short name Ordering. This conflicts with Lean's native Ordering type brought into scope by open Aeneas.Std, causing type mismatches in generated Pre/Post structs.

Aeneas already has the fully-qualified type information in its generated Funs.lean signatures (e.g., core.sync.atomic.Ordering). The spec generator could parse these signatures and use the qualified names as overrides.