[portage] mark as partial, make stub-only type private

Author: Tatsh

stubs/portage/@tests/stubtest_allowlist.txt

@@ -1,5 +1,6 @@
 version = "3.0.*"
 upstream_repository = "https://gitweb.gentoo.org/proj/portage.git"
+partial_stub = true
 
 [tool.stubtest]
-ci_platforms = ["linux"]
+ignore_missing_stub = true

stubs/portage/METADATA.toml

@@ -5,11 +5,11 @@ from .dbapi.porttree import portagetree
 from .package.ebuild.config import config
 
 @type_check_only
-class DBRootDict(TypedDict):
+class _DBRootDict(TypedDict):
     bintree: Any
     porttree: portagetree
     virtuals: Any
 
-db: Mapping[str, DBRootDict]
+db: Mapping[str, _DBRootDict]
 root: str
 settings: config