Resource manifest metadata for parallel execution safety

[theJasonHelmick]

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.

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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.

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Proposal

Add a field to the resource manifest, for example:

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

### Proposed technical implementation details (optional)

_No response_