docs: add comprehensive GitHub Copilot instructions with uv and semantic commit guidelines

[Copilot]

This PR adds a comprehensive .github/copilot-instructions.md file that provides GitHub Copilot coding agents with detailed guidance on how to work effectively in the dpdata repository.

The instructions include:

Package Management with uv:

• Uses uv pip install for all package installations instead of pip
• Provides faster and more reliable dependency management
• Includes troubleshooting for network timeouts and installation issues

Semantic Commit Guidelines:

• Enforces semantic commit message format: type(scope): description
• Defines commit types: feat, fix, docs, style, refactor, test, chore
• Requires semantic format for both commits and PR titles
• Provides clear examples for different scenarios

Core Development Workflow:

• Step-by-step installation process using uv
• Test execution commands with timing expectations (~10 seconds for full suite)
• Linting and formatting using ruff with "NEVER CANCEL" warnings
• Documentation build process using Sphinx

Validated Commands:
All commands have been tested and validated:

• CLI functionality (dpdata --version, dpdata --help)
• Test suite execution (python -m unittest discover)
• Individual test modules (python -m unittest test_<module>.py)
• Code quality tools (ruff check, ruff format)
• Coverage reporting

Key Features:

• Imperative tone throughout with clear directives
• Timing expectations for all operations
• Comprehensive troubleshooting section
• Repository structure overview
• Format-specific development workflows
• Clear validation scenarios for testing changes

Additional Improvements:

• Updated .gitignore to exclude test artifacts (tests/data_*, tests/tmp.*, tests/.coverage)
• Documented core vs optional dependency relationships
• Included guidance for plugin development

The instructions follow GitHub Copilot's expected format with firm directives to reference them first before falling back to search or bash commands.

Fixes #872.

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[njzjz]

@robinzyb It seems you accidentally committed this file in #446. Copilot found and removed it.

[njzjz]

pre-commit.ci autofix

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.47%. Comparing base (5f1dec8) to head (b907a88).
⚠️ Report is 28 commits behind head on devel.

Additional details and impacted files

@@           Coverage Diff           @@
##            devel     #873   +/-   ##
=======================================
  Coverage   85.47%   85.47%           
=======================================
  Files          82       82           
  Lines        7675     7675           
=======================================
  Hits         6560     6560           
  Misses       1115     1115           

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