Adds standardized templates to reduce incomplete issue/PR submissions and improve contributor experience.

Changes

• Issue templates (.github/ISSUE_TEMPLATE/)

  • bug_report.md - Environment (OS, compiler, Vulkan SDK), reproduction steps, expected/actual behavior
  • feature_request.md - Problem statement, use cases, impact analysis
  • question.md - Lightweight template for general inquiries

• Pull Request template (.github/PULL_REQUEST_TEMPLATE.md)

  • Type classification (bug fix, feature, breaking change, etc.)
  • Testing checklist with xmake/clang-format references
  • Documentation update tracking

All templates use YAML frontmatter for automatic labeling and title prefixes.

---

This section details on the original issue you should resolve

<issue_title>Add templates for Issues and Pull Requests</issue_title>
<issue_description>## Problem
The repository lacks dedicated templates for Issues and Pull Requests, which can lead to inconsistent or incomplete reporting and submission by contributors. Having standardized templates improves clarity and speeds up the review process.

Proposal

• Add an Issue template that guides users to provide key information when reporting bugs, requesting features, or asking questions.
• Add a Pull Request template to ensure contributors provide context, testing steps, and any required documentation.

Tasks

• Create a .github/ISSUE_TEMPLATE/ directory if it doesn't exist.
• Add one or more Markdown Issue templates (e.g., bug_report.md, feature_request.md).
• Add a PULL_REQUEST_TEMPLATE.md in .github/ (or as appropriate).
• Ensure templates include clear sections for description, steps to reproduce, expected/actual behavior (issues), and for context, testing, and documentation (PRs).

Acceptance Criteria

• All new Issues and Pull Requests use the new templates by default.
• Templates are clear and help reduce back-and-forth for missing information.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add templates for Issues and Pull Requests #449

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