Improvement: E2E protection for Rust Method/Field APIs

## What
Add E2E (End-to-End) protection for Rust `Method`/`Field` APIs (and, by extension, `Event`). Split out of #782 at @bharatGoswami8's request: https://github.com/eclipse-score/communication/issues/782#issuecomment-5580666403 — out of #782's milestone-1 scope, and no tracking issue existed for it.

## How
Not designed yet. Per the linked comment, E2E protection hasn't been considered so far even for the existing Rust Event implementation, so this needs a design discussion (aligning with whatever E2E mechanism exists on the C++ side, if any) before implementation.

## Estimates for realization
TBD, pending the design discussion above.

## Requirements / Architecture
- [ ] Requirements / Architecture are not affected by this change?

No files or tests are named. Start with the linked discussion in #782, then inspect the existing Rust Event implementation and determine whether the C++ side has an E2E mechanism to align with. Done means agreeing on the E2E design and implementing protection for Rust Method/Field APIs and Event.

Written by the indexing model from the issue text.