Include every repo only once in the $*REPO chain

CompUnitRepo caches repositories by path and will give you the same repo object
for the same path. Since repos are now a linked list, re-using an object from
the end of the list, will give you a rather short chain.

Having a path represented by only a single object is still a good idea. And
there should be no reason to have a path in multiple places of the repo chain,
so avoid the breakage by making sure we include every repo only once.

src/core/Process.pm

@@ -38,7 +38,7 @@ multi sub INITIALIZE_DYNAMIC('$*TMPDIR') {
 
 multi sub INITIALIZE_DYNAMIC('$*REPO') {
     my CompUnit::Repository $next-repo;
-    $next-repo := CompUnitRepo.new($_, :$next-repo) for @*INC.reverse;
+    $next-repo := CompUnitRepo.new($_, :$next-repo) for @*INC.unique.reverse;
     PROCESS::<$REPO> := $next-repo;
 }