Rust MaD: add blanket-impl fallback for sink/source/barrier matching and model GlobalAlloc::realloc

[Copilot]

Blanket-impl trait methods now have canonical paths like <_ as Trait>::method, but Rust MaD sink/source/barrier matching only handled exact path equality. That caused blanket-impl calls (notably GlobalAlloc methods used by std::alloc::System) to miss modeled flow.

• MaD matching parity for non-summary models

  • Extended FlowSourceFromModel, FlowSinkFromModel, FlowBarrierFromModel, and FlowBarrierGuardFromModel to support an implements fallback, mirroring summary-side behavior.
  • Fallback models are emitted as generated provenance to preserve precedence semantics against exact/manual models.

• Dedup guard for concrete impls

  • Constrained fallback to blanket-impl canonical paths (<_ as ...>) so concrete impl methods do not match both exact and inherited paths.

• Missing realloc sink model

  • Added core::alloc::global::GlobalAlloc::realloc sink entry in alloc.model.yml (Argument[2], alloc-size), enabling System.realloc(..) sink coverage.

• Targeted MaD barrier coverage

  • Added trait-method blanket-impl cases in barrier library tests to exercise fallback behavior for barrierModel and barrierGuardModel paths as well.

// ModelsAsData.qll (fallback branch shape)
this.implements(f) and
not this.getCanonicalPath() = path and
this.getCanonicalPath().matches("<_ as %") and
provenance_ = "hq-generated"

# alloc.model.yml
- ["core::alloc::global::GlobalAlloc::realloc", "Argument[2]", "alloc-size", "manual"]