Translation operations are recorded twice via the chat_translation wrapper provider

Problem/Motivation

When ai_translate is configured to use the chat_translation provider,
every translation is recorded twice in ai_metering: once under the non-billable
chat_translation provider name and once under the real provider
(e.g. anthropic). This doubles the call count and the displayed
cost on the dashboard, and surfaces a provider name that has no pricing of its own.

The root cause is that chat_translation is a wrapper: it dispatches
its own PostGenerateResponseEvent and then makes a nested call to
the real provider, which dispatches a second event. ai_metering records both.

Steps to reproduce

1. Install ai_metering and ai_translate. Configure ai_translate to use the chat_translation provider backed by Anthropic.
2. Translate a node (e.g. from English to French).
3. Open /admin/reports/ai-metering. Two rows appear with the same timestamp: one labelled chat_translation and one labelled anthropic. Token counts and cost are doubled.

Environment

• Drupal version: 11.3.11
• ai_metering version: 1.0.0-alpha1
• AI provider module + version: ai_provider_anthropic 1.x
• AI feature module tested: ai_translate 1.x

Proposed resolution

Skip wrapper-provider events in AiPostGenerateSubscriber, keyed off
a small list of known wrapper providers (starting with chat_translation).
The inner call to the real provider already records the operation with the correct
tokens, model, and billable provider, so only that row should remain.

Remaining tasks

• Skip wrapper providers in AiPostGenerateSubscriber.
• Add a kernel test asserting no row is written for a wrapper provider event.
• Verify a single row per translation appears under the real provider.
• Review.

User interface changes

Yes, the dashboard shows one row per translation with the correct provider and cost.

API changes

N/A

Data model changes

N/A

AI assistance

N/A