feat(gateway): check VM host tools during config preflight (#4037)

* feat(gateway): validate VM filesystem tools during preflight

Check required local VM tools through config preflight and share executable
resolution with VM image operations. Report selected paths and actionable
errors without creating gateway or sandbox state.

Bound probe output and execution time, and clean up probe descendants on
interruption. Preserve pure static validation and skip local tool checks
for remote driver endpoints and unrelated drivers.

Fixes #3951
Related to #3955

Signed-off-by: Shiju <shiju@nvidia.com>

* fix(gateway): stabilize filesystem preflight checks

Combine identical filesystem-tool error arms and normalize rendered
diagnostics in command tests so terminal wrapping preserves assertions.
Describe driver TLS validation without depending on removed guest fields.

Signed-off-by: Shiju <shiju@nvidia.com>

* test(gateway): serialize preflight fixture paths as TOML

Keep temporary paths quoted and escaped through the TOML serializer
instead of relying on Rust Debug formatting.

Signed-off-by: Shiju <shiju@nvidia.com>

---------

Signed-off-by: Shiju <shiju@nvidia.com>

Author: shiju-nv

crates/openshell-core/src/e2fsprogs.rs

@@ -17,6 +17,8 @@ pub mod denial;
 pub mod driver_mounts;
 pub mod driver_utils;
 pub mod dynamic_string_allowlist;
+#[cfg(unix)]
+pub mod e2fsprogs;
 pub mod endpoint_path;
 pub mod endpoint_status;
 pub mod error;