Use rpm2cpio for u-boot extraction to avoid 572MB memory spike

rpmfile decompresses the entire zstd CPIO payload (572MB) into memory
to extract a 1.6MB file. On 4Gi VMs running parallel tests this
triggers the OOM killer. Use rpm2cpio + cpio on Linux which streams
without buffering; fall back to rpmfile on macOS.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mangelajo

python/packages/jumpstarter-driver-uboot/jumpstarter_driver_uboot/driver_test.py

@@ -1,5 +1,7 @@
 import os
 import platform
+import shutil
+import subprocess
 
 import pytest
 import requests
@@ -35,12 +37,19 @@ def uboot_image(tmpdir_factory):
         pytest.fail(f"Failed to download u-boot RPM: {e}")
 
     print("Extracting u-boot.bin from RPM...")
-    with rpmfile.open(rpm_path) as rpm:
-        fd = rpm.extractfile("./usr/share/uboot/qemu_arm64/u-boot.bin")
-        with bin_path.open("wb") as f:
-            f.write(fd.read())
+    if shutil.which("rpm2cpio") and shutil.which("cpio"):
+        subprocess.run(
+            f"rpm2cpio {rpm_path} | cpio -idm --quiet ./usr/share/uboot/qemu_arm64/u-boot.bin",
+            shell=True, cwd=str(tmp_path), check=True,
+        )
+        extracted = tmp_path / "usr" / "share" / "uboot" / "qemu_arm64" / "u-boot.bin"
+        extracted.rename(bin_path)
+    else:
+        with rpmfile.open(rpm_path) as rpm:
+            fd = rpm.extractfile("./usr/share/uboot/qemu_arm64/u-boot.bin")
+            with bin_path.open("wb") as f:
+                f.write(fd.read())
     print(f"Extracted u-boot.bin ({bin_path.stat().st_size} bytes)")
-    print("Starting QEMU test...")
 
     yield bin_path