Add CancellationToken support to all async methods

[tw4]

Summary

All public async methods in Nexar lack CancellationToken support. This means long-running HTTP requests cannot be cancelled by the caller.

Affected Methods

• GetAsync<T>()
• PostAsync<T>()
• PutAsync<T>()
• DeleteAsync<T>()
• PatchAsync<T>()
• HeadAsync<T>()
• All corresponding methods in NexarRequestBuilder

Expected Behavior

Each async method should accept an optional CancellationToken cancellationToken = default parameter and pass it down to the underlying HttpClient call.

Example

var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
var response = await Nexar.GetAsync<MyModel>(url, cancellationToken: cts.Token);