tests: split integration helpers into common modules

Move shared integration test logic out of tests/integration.rs.
Add tests/common/{mod.rs,tests_wrappers.rs,utils.rs} and migrate
API, VM lifecycle, disk/net, and utility helpers.

Update integration.rs to import common modules and keep test
entrypoints thin.

Benefits:
 Reduces integration.rs size and duplication
 Groups reusable helpers by role
 Improves readability and future maintenance

Fixes: https://github.com/cloud-hypervisor/cloud-hypervisor/issues/7808

Signed-off-by: Muminul Islam <muislam@microsoft.com>

cloud-hypervisor/tests/common/mod.rs

@@ -0,0 +1,6 @@
+// Copyright 2025 The Cloud Hypervisor Authors. All rights reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+
+pub(crate) mod tests_wrappers;
+pub(crate) mod utils;