Create comprehensive GitHub Copilot instructions for development workflow

[Copilot]

This PR adds a comprehensive .github/copilot-instructions.md file that provides GitHub Copilot coding agents with detailed instructions for working effectively in the trodes_to_nwb codebase.

Key Features

Environment Setup Instructions

• Complete conda environment setup with exact commands and timing expectations
• Documented workaround for pip install issues using PYTHONPATH approach
• Clear timeout guidance (5+ minutes for environment creation, never cancel)

Development Workflow

• Step-by-step commands for setting up a working development environment
• Validation steps to ensure the package works correctly after changes
• Linting and formatting commands with expected timing

Critical Issue Documentation

• Network connectivity issues with PyPI that prevent pip install -e .
• Missing test data files (.rec files) that cause many tests to fail normally
• FFmpeg dependency conflicts between pip and conda versions

Complete Testing Strategy

• Test suite timing expectations (~1-2 minutes, many tests skip due to missing data)
• Basic functionality validation script for core package functionality
• Code formatting validation with black

Practical Examples

• Working example development session with all commands
• Common task reference with repository structure overview
• Before-commit checklist to ensure code quality

The instructions follow an imperative tone with firm directives as requested, providing everything a coding agent needs to work effectively in this scientific data conversion codebase without trial-and-error discovery.

Fixes #137.

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✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.