[CNS-5114] Nlb endpoints tests

[uaggarwa]

📝 Description

What does this PR do and why is this change necessary?
linode-load-balancer-controller requires nlb-endpoints implemented by linodego. We want to move from our fork to main branch.

✔️ How to Test

What are the steps to reproduce the issue or verify the changes?

How do I run the relevant unit/integration tests?

go test ./test/unit -run TestNetLoadBalancer -v
go test ./test/unit -run TestNetLoadBalancerNode -v
go test ./test/unit -run TestNetLoadBalancerListener -v 

📷 Preview

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[Copilot]

Pull Request Overview

This PR adds comprehensive test coverage for NetLoadBalancer endpoints, including operations for load balancers, listeners, and nodes. The implementation includes unit tests for CRUD operations, JSON unmarshaling, edge cases, and conversion methods.

• Adds unit tests for NetLoadBalancer, NetLoadBalancerListener, and NetLoadBalancerNode endpoints
• Implements JSON fixtures to support the test cases
• Includes tests for helper methods (GetCreateOptions, GetUpdateOptions)

Reviewed Changes

Copilot reviewed 30 out of 30 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/unit/netloadbalancer_test.go	Tests for NetLoadBalancer CRUD operations, JSON unmarshaling, and conversion methods
test/unit/netloadbalancer_listeners_test.go	Tests for listener CRUD operations, node weight updates, and edge cases
test/unit/netloadbalancer_nodes_test.go	Tests for node CRUD operations, conversion methods, and edge cases
test/unit/fixtures/*.json	JSON fixtures supporting various test scenarios for load balancers, listeners, and nodes
netloadbalancer.go	Core NetLoadBalancer struct and API methods
netloadbalancer_listeners.go	NetLoadBalancerListener struct and API methods
netloadbalancer_nodes.go	NetLoadBalancerNode struct and API methods

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