Fix token usage not displayed in Namer result

[aslamdoctor]

Summary

Fixes #1220

• Root cause: WP_AI_Client_Prompt_Builder provides methods like generate_text_result() via PHP's __call() magic method. The code used method_exists() which returns false for magic methods, so generate_text_result() was never called. Instead, it always fell through to generate_text() which returns a plain string with no token usage data — resulting in "undefined total" in the UI.
• Fix: Replace method_exists() with is_callable() in execute_ai_request() so the rich result path is used and token usage is returned.
• Fallback: Compute total_tokens from prompt_tokens + completion_tokens in PHP if not directly available, and add defensive JS handling to prevent "undefined total" display.

Screenshot

Test plan

• Go to WP Admin → Tools → Plugin Check Namer
• Enter a plugin name and click Evaluate name
• Verify the Tokens used line displays actual numeric values (e.g. 1,234 total (850 prompt + 384 completion))
• Verify the similar name query token count is also displayed when available

[github-actions]

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Co-authored-by: aslamdoctor <aslamdoctor@git.wordpress.org>
Co-authored-by: davidperezgar <davidperez@git.wordpress.org>
Co-authored-by: raftaar1191 <raftaar1191@git.wordpress.org>

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[raftaar1191]

@aslamdoctor

here with the token I am also see the model name. I think here should be one more section call as Model used

Now:

How I guess it should be:

@davidperezgar what do you think?

[davidperezgar]

Look nice!