fix(e2e): bind wheel server to IPv4 explicitly on macOS

On macOS, python3 -m http.server without --bind calls getaddrinfo()
which returns AF_INET6 first, causing the server to bind to :: (IPv6).
Since macOS defaults IPV6_V6ONLY=1, the IPv6 socket does not accept
IPv4 connections, so uv connecting to 127.0.0.1 gets ETIMEDOUT.

Bind explicitly to 127.0.0.1 on macOS and 0.0.0.0 on Linux (where
podman containers need to reach the server via the host's routable IP).

Also replaces non-POSIX `which` with `command -v`.

Closes: #924
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Lalatendu Mohanty <lmohanty@redhat.com>

Author: LalatenduMohanty

e2e/common.sh

@@ -67,18 +67,20 @@ trap on_exit EXIT SIGINT SIGTERM
 
 start_local_wheel_server() {
     local serve_dir="${1:-$OUTDIR/wheels-repo/}"
-    # Start a web server for the wheels-repo. We remember the PID so we
-    # can stop it later, and we determine the primary IP of the host
-    # because podman won't see the server via localhost.
-    python3 -m http.server --directory "$serve_dir" 9999 &
-    HTTP_SERVER_PID=$!
-    if which ip 2>&1 >/dev/null; then
-        # Linux: need host IP because podman can't reach localhost
+    # Determine the bind address and the URL that clients will use.
+    # On Linux podman can't reach localhost, so we bind to 0.0.0.0 and
+    # advertise the host's routable IP.  On macOS there is no network
+    # isolation; we bind explicitly to 127.0.0.1 to avoid IPv6-only
+    # sockets that python3 -m http.server may create by default.
+    if command -v ip >/dev/null 2>&1; then
+        local BIND_ADDR="0.0.0.0"
         IP=$(ip route get 1.1.1.1 | grep 1.1.1.1 | awk '{print $7}')
     else
-        # macOS: no network isolation, localhost works
+        local BIND_ADDR="127.0.0.1"
         IP=127.0.0.1
     fi
+    python3 -m http.server --bind "$BIND_ADDR" --directory "$serve_dir" 9999 &
+    HTTP_SERVER_PID=$!
     export WHEEL_SERVER_URL="http://${IP}:9999/simple"
 
     # Wait for the server to accept connections (up to 15 s).