Add CopyFrom for VPC subnet model

[zliang-akamai]

📝 Description

Implementing CopyFrom for VPCSubnetModel

✔️ How to Test

make PKG_NAME="vpcsubnet" test-int

[Copilot]

Pull Request Overview

This PR implements the CopyFrom method for the VPCSubnetModel struct to facilitate copying values between model instances. The changes also include consistent renaming of variable names from vpcId to vpcID for better Go naming conventions and field name updates from VPCId to VPCID.

• Added CopyFrom method to VPCSubnetModel for copying field values between instances
• Renamed variables and struct fields from vpcId/VPCId to vpcID/VPCID for consistency
• Updated the Update method to use CopyFrom instead of manual attribute retrieval

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
linode/vpcsubnet/framework_resource.go	Updated variable names and replaced manual state copying with CopyFrom method call
linode/vpcsubnet/framework_models.go	Added CopyFrom method and renamed struct field from VPCId to VPCID
linode/vpcsubnet/framework_datasource.go	Updated variable name from vpcId to vpcID for consistency

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[jriddle-linode]

LGTM