TPT-4462: Support VPC RDMA Interfaces

[yec-akamai]

📝 Description

Add support to specify VPC type and RDMA VPC. Allow to create the RDMA intercase with the instance creation. Allow to change the RDMA interface with the interface object.

✔️ How to Test

make test-unit

[Copilot]

Pull request overview

Adds SDK support for RDMA-capable VPCs by introducing a VPC type field and RDMA VPC Linode interface structures, plus corresponding unit/fixture updates.

Changes:

• Add vpc_type support to VPC objects and VPC create requests (with VPCType enum).
• Add RDMA VPC (rdma_vpc) interface option/response models and unit tests for GET/PUT + instance-create serialization.
• Extend fixtures and a small integration-test import cleanup to keep tests passing.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/unit/objects/vpc_test.py	Adds assertions + create-request tests for vpc_type handling.
test/unit/objects/linode_interface_test.py	Adds RDMA VPC interface option builder and GET/PUT unit coverage.
test/unit/groups/linode_test.py	Adds instance-create unit coverage for RDMA VPC interface serialization.
test/integration/models/networking/test_networking.py	Import formatting cleanup only.
test/fixtures/vpcs.json	Adds vpc_type to VPC list fixture.
test/fixtures/vpcs_123456.json	Adds vpc_type to VPC detail fixture.
test/fixtures/vpcs_123456_subnets.json	Adds vpc_type to VPC subnets list fixture.
test/fixtures/vpcs_123456_subnets_789.json	Adds vpc_type to VPC subnet detail fixture.
test/fixtures/linode_instances_124_interfaces_999.json	New fixture for RDMA VPC Linode interface GET response.
linode_api4/objects/vpc.py	Introduces VPCType and maps vpc_type onto VPC/VPCSubnet properties.
linode_api4/objects/region.py	Adds gpudirect_rdma region capability enum value.
linode_api4/objects/linode.py	Documents RDMA interface creation limitation on interface_create.
linode_api4/objects/linode_interfaces.py	Adds RDMA VPC option/response JSONObject models + LinodeInterface.rdma_vpc property.
linode_api4/groups/vpc.py	Adds vpc_type parameter to VPC create and forwards it to the API.

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[ezilber-akamai]

LGTM and tests passed locally. Nice work!