Rust: Fix candidate receiver type calculation for trait bounds

[hvitved]

When inferring call targets involving traits bounds such as

fn foo<T : Bar + Baz>(x : T) {
  x.m();
}

we substitute in the trait bounds in the receiver type (using substituteLookupTraits), meaning we treat x as having both types Bar and Baz. That is, we attempt to lookup m in both Bar and Baz. However, when computing candidate receiver types we should only progress to &Bar and &Baz when m cannot be found in both Bar and Baz, which previously was implemented as either Bar or Baz.

This PR fixes the issue above, and as usual we use ranked recursion to implement efficient forex.

DCA is fine.

[Copilot]

Pull request overview

This PR fixes a bug in the Rust type inference for trait bounds where method lookup incorrectly required finding a method in either trait bound instead of requiring it to be absent from both trait bounds before progressing to the next candidate receiver type (e.g., from Bar and Baz to &Bar and &Baz). The fix uses ranked recursion to efficiently implement the "for all exists" (forex) pattern needed for this check.

Key changes:

• Introduced getNthLookupType and getLastLookupTypeIndex helper predicates to enumerate trait bounds in a deterministic order
• Refactored the hasNoCompatibleTarget* predicates to use recursive predicates that check all trait bounds using ranked recursion
• Added test case demonstrating the fix with overlapping trait bounds

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
rust/ql/lib/codeql/rust/internal/typeinference/FunctionType.qll	Added helper predicates getNthLookupType and getLastLookupTypeIndex to enumerate lookup traits in a deterministic order for efficient forex implementation
rust/ql/lib/codeql/rust/internal/TypeInference.qll	Refactored method resolution predicates to use recursive helpers that check all trait bounds rather than just one, implementing the correct "all traits" semantics
rust/ql/test/library-tests/type-inference/main.rs	Added test case bound_overlap demonstrating trait bounds with overlapping method names correctly resolved based on receiver type
rust/ql/test/library-tests/type-inference/blanket_impl.rs	Updated test expectation from MISSING to correctly identifying S1::m1 as the resolution target
rust/ql/test/library-tests/type-inference/CONSISTENCY/PathResolutionConsistency.expected	Updated line numbers to reflect additions to main.rs test file

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[Copilot]

Spelling error: "abitrary" should be "arbitrary".

Suggested change

	* Gets the `n`th `substituteLookupTraits` type for `t`, per some abitrary order.
	* Gets the `n`th `substituteLookupTraits` type for `t`, per some arbitrary order.