feat: subprocess support, networking idle-poll fix, and CI improvements

[danbugs]

Add subprocess support for the Hyperlight platform via vfork/execve, enabling
Python's subprocess.run() to execute busybox commands and pip installs inside
the guest. Since Hyperlight has no MMU, fork() is promoted to vfork
(CLONE_VM | CLONE_VFORK) — the child shares the parent's address space.

• Increase heap to 2.5 GiB for subprocess memory requirements
• Point python-agent-driver kraft.yaml at upstream unikraft/app-elfloader plat-hyperlight
• Add busybox and pip install demo scripts with CI regression tests
• Build base Docker images automatically in just rootfs
• Replace strtoul with inline hex parser (no libc dependency in hl_pydriver)
• Add urllib GET without timeout test for idle-poll networking path
• Add per-test timeout wrapper to Windows CI runtime tests

[Copilot]

Pull request overview

This PR updates the Python agent driver example and host tooling to better support subprocess-style workflows (pip installs and running basic shell utilities inside the guest), along with a small adjustment to socket polling behavior during guest sleep.

Changes:

• Narrow poll/WSAPoll event masks used by __hl_sleep socket polling while sleeping.
• Increase the warm-up sandbox heap size used during pyhl setup.
• Update the python-agent-driver example rootfs and build inputs to support pip installs (offline wheels) and BusyBox-based subprocess demos.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
host/src/lib.rs	Adjusts socket poll event masks used during sleep to avoid polling for writability.
host/src/bin/pyhl.rs	Increases the fixed heap size used for the warm-up/snapshot sandbox during pyhl setup.
examples/python-agent-driver/kraft.yaml	Switches Unikraft/app-elfloader sources to a fork/feature branch and enables additional process/FD config.
examples/python-agent-driver/hl_pydriver.c	Adds hex parsing helper and changes how kernel-provided pointer env vars are parsed.
examples/python-agent-driver/Dockerfile	Adds offline wheel download, restores pip + needed stdlib pieces, and adds BusyBox + supporting rootfs setup.
examples/python-agent-driver/demo_pip_install.py	Adds a demo that installs/imports six via pip at runtime in the guest.
examples/python-agent-driver/demo_busybox.py	Adds a demo that runs basic BusyBox commands via subprocess in the guest.

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[github-actions]

Linux Benchmarks

Details

Benchmark suite	Current: 8084df2	Previous: 682ad20	Ratio
hello_world (median)	20 ms	20 ms	1
pandas (median)	110 ms	120 ms	0.92
density (per VM)	11 MB	8 MB	1.38
snapshot (disk)	702 MiB	653 MiB	1.08

This comment was automatically generated by workflow using github-action-benchmark.

[github-actions]

Windows Benchmarks

Details

Benchmark suite	Current: 8084df2	Previous: 682ad20	Ratio
hello_world (median)	354 ms	291 ms	1.22
pandas (median)	1095 ms	1024 ms	1.07
density (per VM)	11 MB	7 MB	1.57
snapshot (disk)	728 MiB	661 MiB	1.10

This comment was automatically generated by workflow using github-action-benchmark.