Update child handle validation in core_disconnect_controller() [Rebase & FF]

[makubacki]

Description

The first commit is the actual change and the second consolidates and cleans up related test code.

---

Update child handle validation in core_disconnect_controller()

Previously, when a specific child handle was requested but was not a
child created by a driver managing the controller, that driver was not
skipped. When the driver had no children its Stop() was still
invoked, and the function reported success even though nothing was
disconnected.

This change:

1. Skips a driver when a specific child handle is requested but is not
   present in that driver's child list (checked via child_handles
   being empty after filtering). When no managing driver owns the
   child, the call returns NotFound.

2. Uses total_children == child_handles.len() to detect that the
   requested child was the driver's only child, in which case the
   driver itself is disconnected (Stop() with zero children). This
   matches the UEFI spec's "if ChildHandle is the only child ... the
   driver will be disconnected" behavior.

Three unit tests are added:

• test_disconnect_specific_child_not_managed_by_driver(): Checks
  that a specific child not owned by the single managing driver
  returns NotFound and Stop() is never called.

• test_disconnect_specific_child_among_multiple_children(): Checks
  that a specific child among several is destroyed (Stop() called
  with that one child) while the driver-level Stop() is not called,
  so the driver stays connected.

• test_disconnect_specific_child_not_owned_by_either_driver(): Checks
  that when two drivers are managing the controller and a child owned
  by neither is requested, that both drivers are skipped and NotFound
  is returned.

Note: EFI_NOT_FOUND is not listed as a return value in for
DisconnectController() in the UEFI 2.11 spec (section 7.3.13), but
returning it when the requested child is unmanaged matches EDK II
behavior.

---

patina_dxe_core: Consolidate disconnect controller test setup logic

The child-specific core_disconnect_controller() tests each repeated
a lot of related logic to install a driver binding, mark the driver as
managing the controller, and register its children.

This commit adds two test helpers, new_test_handle() and
setup_driver_managing_controller() to reduce the overall size of
test functions.

---

• Impacts functionality?
• Impacts security?
• Breaking change?
• Includes tests?
• Includes documentation?

How This Was Tested

• Run all unit tests
• Check that test_disconnect_specific_child_not_managed_by_driver() fails without the change and passes with it
• QEMU boot to EFI shell

Integration Instructions

• N/A

[codecov]

Codecov Report

❌ Patch coverage is 83.52941% with 28 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
patina_dxe_core/src/driver_services.rs	83.53%	28 Missing ⚠️

📢 Thoughts on this report? Let us know!

[patina-automation]

✅ QEMU Validation Passed

All QEMU validation jobs completed successfully.

Note: Q35 is only built on Windows hosts (QEMU boot is disabled due to a QEMU vfat issue).

Workflow run: https://github.com/OpenDevicePartnership/patina/actions/runs/29451283566

Boot Time to EFI Shell

Platform	Elapsed
ArmVirt (Linux Host)	26.6s
Q35 (Linux Host)	25.6s

Dependencies

Repository	Ref
patina	483270c
patina-dxe-core-qemu	423b4ab
patina-fw-patcher	4c7f2e0
patina-qemu firmware	v4.0.3
patina-qemu build script	fb7b09d

This comment was automatically generated by the Patina QEMU PR Validation Post workflow.

[makubacki]

@Javagedes, @os-d, @joschock, I finally returned to rebase this PR and clean up some test logic. Can someone please review again?