Add comprehensive GitHub Copilot instructions for HTML::Parser development

[Copilot]

This PR adds a comprehensive .github/copilot-instructions.md file to guide GitHub Copilot coding agents on how to work effectively with the HTML::Parser codebase.

What's included

The instructions provide exhaustive guidance covering:

• Build system: Complete workflow using ExtUtils::MakeMaker with documented timing expectations
• Testing: 464 tests across 50 test files with validation commands
• Project structure: Detailed breakdown of key modules and directories
• Validation scenarios: Manual testing procedures to ensure changes work correctly
• Performance expectations: Documented build times (~1.5s) and test execution (~3s)
• Common tasks: Ready-to-use commands for development workflows

Key features

The instructions start with a firm directive to follow the documented procedures first before searching for additional context, as requested. All commands have been validated to work correctly, including:

# Complete build and test workflow
perl Makefile.PL && make && make test

# Module functionality validation
perl -MHTML::Parser -e 'print "HTML::Parser loads successfully\n"'

# Example script testing
perl eg/htext test.html

The file includes explicit "NEVER CANCEL" warnings for build operations and proper timeout expectations to prevent premature cancellation of legitimate processes.

Manual validation performed

• Tested complete build workflow from clean state
• Verified all example scripts work correctly
• Validated entity handling and parsing functionality
• Confirmed all documented commands execute successfully
• Measured actual timing for all operations

This provides GitHub Copilot agents with everything needed to work confidently in the HTML::Parser codebase without trial-and-error exploration.

Fixes #53.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• cpanmin.us

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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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.

[Copilot]

@oalders 👋 This repository doesn't have Copilot instructions. With Copilot instructions, I can understand the repository better, work faster and produce higher quality PRs.

I can generate a .github/copilot-instructions.md file for you automatically. Click here to open a pre-filled issue and assign it to me. I'll write the instructions, and then tag you for review.