Fix dyn T resolution ICE

[ninehusky]

Closes #1519.

[Copilot]

Pull request overview

This PR fixes an internal compiler error (ICE) that occurred when resolving associated refinements on dyn trait types. The issue arose because trait resolution for dyn Trait types falls into the builtin implementation path, but user-defined traits on dyn types don't have builtin refinement bodies, causing a panic when the code expected one.

Changes:

• Added a test case that reproduces the ICE scenario from issue #1519
• Added an early return in normalize_alias_reft to handle dyn trait types by treating them as unresolvable aliases

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
tests/tests/pos/surface/no_panic07.rs	Regression test demonstrating the fixed ICE when using associated refinements with dyn trait objects
crates/flux-infer/src/projections.rs	Added check to detect dyn trait types and return them as unresolved aliases instead of attempting builtin resolution

[nilehmann]

Superseded by #1522