Resource manifest metadata for parallel execution safety

Summary of the new feature / enhancement

Introduce a field in the DSC resource manifest that allows a resource author to declare whether multiple instances of the same resource can be safely executed concurrently.

This is an advisory signal only and does not change DSC engine behavior.

Motivation

During discussion of parallel execution (see #42), we agreed that:

• The DSC engine should remain deterministic and sequential
• Parallel orchestration is the responsibility of higher-order tools
• However, higher-order tools need signals from resource authors to make safe decisions

Today, there is no standard way for a resource to indicate whether it is safe to run concurrently with other instances of itself.

Proposal

Add a field to the resource manifest, for example:

{
  "capabilities": {
    "parallelSafe": true
  }
}

### Proposed technical implementation details (optional)

_No response_

No files or tests are named. Start by locating the resource manifest definition, parsing, and validation tests, then trace how manifest metadata is exposed to higher-order tools. Done means the manifest accepts and preserves an advisory parallel-safety field without changing DSC engine execution behavior, with coverage for the new metadata.