fix: reduce EAPI helpers paths to just what's unique.

The previous code stacked each level of inheritance on, resulting
in many duplicates; path look chooses leftmost, thus filter
it down so a directory is only listed once, in the order it
was first exposed.

Signed-off-by: Brian Harring <ferringb@gmail.com>

Author: ferringb

src/pkgcore/ebuild/eapi.py

@@ -11,6 +11,7 @@
 from snakeoil.mappings import ImmutableDict, OrderedFrozenSet, inject_getitem_as_getattr
 from snakeoil.osutils import pjoin
 from snakeoil.process.spawn import bash_version
+from snakeoil.sequences import stable_unique
 
 from typing import Iterable
 
@@ -466,7 +467,7 @@ def helpers(self):
                         paths[phase].append(dirpath)
                     else:
                         raise ValueError(f"unknown phase: {phase!r}")
-        return ImmutableDict((k, tuple(v)) for k, v in paths.items())
+        return ImmutableDict((k, tuple(stable_unique(v))) for k, v in paths.items())
 
     @klass.jit_attr
     def ebd_env(self):