BlockProof and event_metadata protobuf docs/naming

Nobody has claimed this yet.

### Background

> nit: is there an applicable range or mapping the id takes or is it just a monotonically increasing value for every new HinTS scheme?
> Also if there's specification around how often it change you can note.
> This will help devs understand it's usage

Let's add additional information in the comment.

> Q: Should the file be `event_header.proto` or is it intended more metadata would be encompassed here. In the HIP for block streams its `event_header.proto` so checking which name we should be going with.

This could align with the HIP.

### Acceptance Criteria

1. Above details/naming addressed.

### Dependencies

_No response_

### Definition of Ready (DoR) Checklist

- [ ] Clear acceptance criteria
- [ ] Clear and detailed description
- [ ] Dependencies identified
- [ ] Links to documentation
- [ ] Should be completable in 2-3 Days
- [ ] Initial draft of Low-level design document
- [ ] At least high level test plan
- [ ] Groomed/Estimated

### Definition of Done (DoD) Checklist

- [ ] Acceptance Criteria complete
- [ ] No Codacy issues greater than minor (in new code)
- [ ] JavaDocs updated/created
- [ ] Code commented
- [ ] Unit tests created/updated
- [ ] 80% test code coverage (in new code)
- [ ] Happy Path and major negative cases in HAPI tests as applicable

Locate the BlockProof and event_metadata protobuf definitions and compare their naming with the block-stream HIP. Review the existing comments and the HIP guidance for the id range, mapping, and change frequency; done means those details are documented and the file name is aligned or clarified.

Written by the indexing model from the issue text.