pycross: Rename `pycross_wheel_library` and make it work (#1413)

This patch changes the name of the rule to reflect the fact that it's
not exactly the same as the one in rules_pycross.

I also took this opportunity to delete the superfluous
`namespace_pkgs.py` library (plus test) since we have a nearly
identical version already in the main repo.

I added a test to validate that the rule functions at a basic level.

References: #1360

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 9412367..6e1e5fc 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -34,7 +34,7 @@
     python_versions = MINOR_MAPPING.values(),
 )
 
-load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive", "http_file")
 
 # Used for Bazel CI
 http_archive(
@@ -86,3 +86,14 @@
 load("@publish_deps//:requirements.bzl", "install_deps")
 
 install_deps()
+
+# This wheel is purely here to validate the wheel extraction code. It's not
+# intended for anything else.
+http_file(
+    name = "wheel_for_testing",
+    downloaded_file_path = "numpy-1.25.2-cp311-cp311-manylinux_2_17_aarch64.manylinux2014_aarch64.whl",
+    sha256 = "0d60fbae8e0019865fc4784745814cff1c421df5afee233db6d88ab4f14655a2",
+    urls = [
+        "https://files.pythonhosted.org/packages/50/67/3e966d99a07d60a21a21d7ec016e9e4c2642a86fea251ec68677daf71d4d/numpy-1.25.2-cp311-cp311-manylinux_2_17_aarch64.manylinux2014_aarch64.whl",
+    ],
+)