WIP: net: Introduce dual-stream primary network tests

[azhivovk]

Short description:

New dual-stream tests: primary network scenarios

More details:

STD: #4569

What this PR does / why we need it:

Added automation for new dual-stream tests

Which issue(s) this PR fixes: -

Special notes for reviewer:

Follow-up implementation of new tests of primary network
Do not review the first infra commit - it'll be merged in first PR of this series #4772

jira-ticket: https://redhat.atlassian.net/browse/CNV-86194

Summary by CodeRabbit

• New Features

  • Added node selector support for virtual machines, enabling pod pinning to specific Kubernetes nodes.

• Tests

  • Introduced test infrastructure and fixtures for validating connectivity across mixed RHCOS 9 and RHCOS 10 environments.
  • Added pytest marker for tests requiring dual-stream operating system clusters.

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📝 Walkthrough

Walkthrough

This PR adds VM node pinning and test fixtures to enable live migration testing across RHCOS 9 and RHCOS 10 clusters. Changes span VM spec enhancements, node selection utilities, factory function updates, test fixtures, and executable migration tests that validate primary-network connectivity after server VM migration between OS versions.

Changes

RHCOS 9/10 Live Migration Test Infrastructure

Layer / File(s)	Summary
VM Spec Schema libs/vm/spec.py	Adds optional nodeSelector: dict[str, str] | None field to VMISpec for capturing node affinity labels.
Test Markers pytest.ini	Defines mixed_os_nodes marker for tests requiring dual-stream RHCOS 9 and RHCOS 10 worker clusters.
Node Selection Library tests/network/libs/nodes.py	New module with RHCOS_9_VERSION_PREFIX, RHCOS_10_VERSION_PREFIX constants; node_by_rhcos_version() scans workers and returns first match by OS version; update_vm_node_selector() patches VM spec to pin by hostname.
VM Factory Node Support tests/network/libs/vm_factory.py, tests/network/localnet/liblocalnet.py	udn_vm() and localnet_vm() now accept optional node parameter; when provided, sets spec.template.spec.nodeSelector to {kubernetes.io/hostname: node.hostname}, otherwise applies anti-affinity.
Network Test Fixtures tests/network/conftest.py	Adds rhcos9_node and rhcos10_node module-scoped fixtures via node_by_rhcos_version() to select workers by OS version.
Primary Network Fixtures & Helpers tests/network/primary_network/rhel9_rhel10_cluster/conftest.py, tests/network/primary_network/rhel9_rhel10_cluster/lib_helpers.py	New primary_network_vm() factory creates Fedora VMs pinned to a specific node with masquerade-only networking; primary_server_vm and primary_client_vm fixtures start VMs and wait for guest agent connectivity.
Connectivity Tests tests/network/primary_network/rhel9_rhel10_cluster/test_connectivity.py	Removes __test__ = False and implements executable tests: test_primary_connectivity_reestablished_after_server_migration_to_rhcos10 and test_primary_connectivity_reestablished_after_server_migration_to_rhcos9 now accept VM and node fixtures, perform live migration, resolve server IP, and ping from client to verify connectivity after migration.

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🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 60.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Title check	❓ Inconclusive	The title uses 'WIP:' prefix and is vague about the core changes; 'dual-stream primary network tests' doesn't clarify what infrastructure was added or changed.	Remove 'WIP:' and be specific: e.g., 'net: Add nodeSelector support and dual-stream primary network connectivity tests' or split into two focused PRs if infrastructure and tests are distinct efforts.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The pull request description covers all required template sections with relevant details about the dual-stream tests, objectives, and related tracking information.

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[azhivovk]

Change: rebase

[azhivovk]

Change: Drop udn and localnet changes

[azhivovk]

/wip

[azhivovk]

Change:

• Move shared IPv6 masquerade config
• Add IPv6 testing
• Remove redundant comments
• Add back the STD docstring