fix(vm-driver): fixes BYOC sandbox creation failing with ext4-fs writ…

[bornav]

Summary

Fix BYOC sandbox creation failing with "EXT4-fs (vdc): write access unavailable, cannot proceed" under the VM driver by cleanly unmounting the overlay filesystem before the image-prep VM exits, preventing the ext4 journal from being left in a dirty state. Adds noload to the image-cache mount and attaches the disk as hypervisor-writable as belt-and-suspenders so a dirty journal never blocks the mount.

Related Issue

Closes #2149

Changes

changing how VM driver creates container

Testing

• mise run pre-commit passes | check comment

• Unit tests added/updated

• E2E tests added/updated (if applicable)

• manually tested before and after patch if it fixes the issue

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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[bornav]

mise run pre-commit fails both on main and with my patch with error:

[test:rust] test l7::rest::tests::relay_response_no_framing_event_stream_survives_idle_gap ... ok
[test:rust]
[test:rust] failures:
[test:rust]
[test:rust] ---- procfs::tests::binary_path_preserves_live_deleted_basename stdout ----
[test:rust]
[test:rust] thread 'procfs::tests::binary_path_preserves_live_deleted_basename' (303235) panicked at crates/openshell-supervisor-network/src/procfs.rs:662:48:
[test:rust] called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }
[test:rust] note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
[test:rust]
[test:rust] ---- procfs::tests::binary_path_strips_deleted_suffix stdout ----
[test:rust]
[test:rust] thread 'procfs::tests::binary_path_strips_deleted_suffix' (303237) panicked at crates/openshell-supervisor-network/src/procfs.rs:608:48:
[test:rust] called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }
[test:rust]
[test:rust] ---- procfs::tests::binary_path_strips_suffix_for_non_utf8_filename stdout ----
[test:rust]
[test:rust] thread 'procfs::tests::binary_path_strips_suffix_for_non_utf8_filename' (303238) panicked at crates/openshell-supervisor-network/src/procfs.rs:705:48:
[test:rust] called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }
[test:rust]
[test:rust]
[test:rust] failures:
[test:rust]     procfs::tests::binary_path_preserves_live_deleted_basename
[test:rust]     procfs::tests::binary_path_strips_deleted_suffix
[test:rust]     procfs::tests::binary_path_strips_suffix_for_non_utf8_filename
[test:rust]
[test:rust] test result: FAILED. 829 passed; 3 failed; 0 ignored; 0 measured; 0 filtered out; finished in 6.02s
[test:rust]
[test:rust] error: test failed, to rerun pass `-p openshell-supervisor-network --lib`
Finished in 48.05s
[test:rust] ERROR task failed

[bornav]

I have read the DCO document and I hereby sign the DCO.

[bornav]

recheck