[Fn][Observability] Status of OpenTelemetry metrics support (PIP-264/PIP-320)

### Search before reporting

- [x] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### Motivation

## Background ##
Per PIP-264 and PIP-320 , it looks like Pulsar Functions metrics are still not integrated with OpenTelemetry in practice.
Function Worker has PulsarWorkerOpenTelemetry creating a Meter, but Functions-related OTel metrics are not registered/emitted yet .

## Question ##
Could someone clarify the current status of OpenTelemetry metrics for Pulsar Functions?

* If nobody is actively working on it, I’m happy to contribute.

### Solution

_No response_

### Alternatives

_No response_

### Anything else?

_No response_

### Are you willing to submit a PR?

- [x] I'm willing to submit a PR!

Start by reviewing PIP-264 and PIP-320, then inspect the Function Worker’s PulsarWorkerOpenTelemetry class and the existing Functions metrics paths. Determine whether Functions-related OpenTelemetry metrics are registered and emitted; done means documenting the current status and establishing a concrete, agreed scope if support is still missing.

Written by the indexing model from the issue text.