TPT-4602: Support NAT service int tests

[mawilk90]

📝 Description

Created integration tests for VPC NAT Gateway service.

Notes:

1. Please check the API spec for the required Linode account configuration.
2. Reported issue VPC-6253 - unskip dedicated test when resolved

✔️ How to Test

make test-int TEST_ARGS="-k nat_gateway"

[Copilot]

Copilot review overview

🟡 Changes recommended

Unresolved moderate findings affect resource cleanup, regional placement, interface selection, and settings assertions.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 3

Open (3)

• Handle missing resources without masking other API errors · New
• Select the VPC interface instead of the default public interface · New
• Create the reserved IP in the NAT gateway's region · New

What changed in this PR

Adds integration coverage for VPC NAT Gateway functionality.

Changes:

• Adds NAT Gateway and VPC subnet integration tests.
• Adds NAT Gateway, VPC, subnet, and Linode fixtures.
• Covers lifecycle, address assignment, interfaces, types, and settings.

File	Description
test/​integration/​models/​vpc/​test_vpc.py	Tests NAT Gateway attachment to VPC subnets.
test/​integration/​models/​networking/​test_networking.py	Adds NAT Gateway operation and settings tests.
test/​integration/​conftest.py	Adds NAT-related integration fixtures.

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[ezilber-akamai]

Tests are passing locally and look good. Nice work!

[Copilot]

Copilot review overview

🟡 Changes recommended

Several integration tests contain incorrect interface, region, error-message, and teardown handling.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 2

Open (2)

• Clean up reserved IP assignment during teardown · New
• Compare region IDs instead of Region objects · New

Resolved since last review (3)

• Create the reserved IP in the NAT gateway's region
• Select the VPC interface instead of the default public interface
• Handle missing resources without masking other API errors

Previously missed (1)

In code that hasn't changed since last review

Compares against the wrong Linode interface

test/​integration/​models/​networking/​test_networking.py:227

The Linode is created before the new VPC interface, so its existing public interface remains at index 0; the NAT gateway interface is not linode.linode_interfaces[0] (the repository's interface tests establish public first and VPC second). This compares against the wrong interface and will fail; compare with the newly created interface or verify membership instead.