Refactor Claude Endpoint, introduce Must0 utility, and add tests

[nvtrinh2001]

Summary

This PR does:

• refactor the Claude Endpoint implementation to use dependency injection (DI) instead of directly coupling to the anthropic.Client struct
• add tests for Claude Endpoint
• add util function Must0 to guarantee not producing errors
• add tests for Must0

[seungduk-yanolja]

The convention is to have a test file for each go file.

[nvtrinh2001]

@seungduk-yanolja thank you for the feedback. For the Ping and GenerateChatCompletion methods, since the client field in Endpoint is not an interface, but a pointer to the anthropic.Client struct, I cannot inject mock to create unit tests for them.

Here is the current code:

type Endpoint struct {
	client *anthropic.Client
}
func (ep *Endpoint) Ping(ctx context.Context) (time.Duration, error) {
	start := time.Now()
	_, err := ep.client.Messages.New(ctx, anthropic.MessageNewParams{
		Model:     anthropic.F(anthropic.ModelClaude_3_Haiku_20240307),
		MaxTokens: anthropic.Int(1),
		Messages: anthropic.F([]anthropic.MessageParam{
			anthropic.NewUserMessage(anthropic.NewTextBlock("Ping")),
		}),
	})
	if err != nil {
		return 0, err
	}
	return time.Since(start), nil
}

What is your recommendation to solve it? Should I change the current code to make it easier to test, or ignore it and write integration test with real API call instead?

[nvtrinh2001]

@seungduk-yanolja I updated the claude.go file to be more testable. I also wrote a test file for it and removed unnecessary tests for private methods.

[seungduk-yanolja]

Please capitalize the first letter of the PR title