Configure nuget-release workflow to validate PRs without publishing

[Copilot]

The nuget-release.yml workflow only ran on direct pushes to master/release or tags, meaning PRs weren't validated by CI before merge.

Workflow Changes:

• Added pull_request trigger for master and release branches
• Gated NuGet publishing step with github.event_name != 'pull_request' condition

Behavior:

• PRs: Build, test, and upload artifacts for validation - no publishing
• Merges/Tags: Full workflow including NuGet publishing

on:
  push:
    branches: ['master', 'release']
    tags: ['[0-9]+.[0-9]+.[0-9]+']
  pull_request:
    branches: ['master', 'release']

# ...

- name: Push to NuGet
  if: success() && matrix.os == 'windows-latest' && github.event_name != 'pull_request'

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