internal/rosa: drop caches

This enables accurate benchmarking of the toolchain abstraction.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/all.go

@@ -307,6 +307,17 @@ var (
 	artifactsOnce [_toolchainEnd][len(artifactsM)]sync.Once
 )
 
+// zero zeros the value pointed to by p.
+func zero[T any](p *T) { var v T; *p = v }
+
+// DropCaches arranges for all cached [pkg.Artifact] to be freed some time after
+// it returns. Must not be used concurrently with any other function from this
+// package.
+func DropCaches() {
+	zero(&artifacts)
+	zero(&artifactsOnce)
+}
+
 // GetMetadata returns [Metadata] of a [PArtifact].
 func GetMetadata(p PArtifact) *Metadata { return &artifactsM[p] }