Add support for VPCSubnet.databases field

[lgarber-akamai]

📝 Description

This pull request adds support for the databases field returned for VPC subnets with attached Managed Databases.

✔️ How to Test

The following test steps assume you have pulled down this PR locally and run make install.

Unit Testing

make test-unit

Manual Testing

1. In a linode_api4-python sandbox environment (e.g. dx-devenv), run the following:

import os

from linode_api4 import (
    LinodeClient,
    DatabasePrivateNetwork,
)

linode_client = LinodeClient(
    os.getenv("LINODE_TOKEN"), base_url="https://api.linode.com/v4beta"
)

vpc = linode_client.vpcs.create(label="python-sdk-test", region="us-mia")

subnet = vpc.subnet_create(label="python-sdk-test", ipv4="10.0.0.0/24")

db = linode_client.database.mysql_create(
    label="python-sdk-test",
    ltype="g6-nanode-1",
    region="us-mia",
    engine="mysql/8",
    private_network=DatabasePrivateNetwork(
        vpc_id=vpc.id, subnet_id=subnet.id, public_access=False
    ),
)

subnet.invalidate()

print(subnet.databases)

2. Ensure the output looks similar to the following:

[VPCSubnetDatabase(id=365862, ipv4_range='10.0.0.16/28', ipv6_range=None)]

[zliang-akamai]

Looks good and works well!

[yec-akamai]

Works well on my end!

[Copilot]

Pull Request Overview

This PR adds support for the databases field in VPC subnets to handle Managed Databases attached to VPC subnets. The implementation includes a new VPCSubnetDatabase class and corresponding property mapping.

• Adds VPCSubnetDatabase data class to represent database information within VPC subnets
• Updates VPCSubnet class to include the databases property
• Adds comprehensive test coverage including fixtures and validation

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
linode_api4/objects/vpc.py	Adds VPCSubnetDatabase class and databases property to VPCSubnet
test/unit/objects/vpc_test.py	Adds test validation for databases field functionality
test/fixtures/vpcs_123456_subnets_789.json	Adds test fixture data for single subnet with database
test/fixtures/vpcs_123456_subnets.json	Adds test fixture data for subnet list with database

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