Alchemy discoballed directive

[AryaHassanli]

• Introduce the :alchemy-discoballed: directive; files with this directive at the top are considered already discoballed.
• Update disco templates to suggest optional fixes and enforce mandatory ones.
• Implement logic to distinguish between optional and mandatory fixes. Mandatory fixes apply to files that either have the :alchemy-discoballed: directive or are newly added to the repository.

[gemini-code-assist]

Code Review

This pull request introduces a tiered enforcement system for 'disco-ball' suggestions, distinguishing between mandatory and optional fixes based on whether a file is new or already contains the :alchemy-discoballed: marker. Key changes include updating the GitHub Action to handle multiple patch outputs, introducing a combined template for PR comments, and automating the placement of the marker at the top of files. Review feedback identified critical issues regarding potential nil pointer dereferences in GitHub API interactions, imprecise marker detection logic, and the incorrect application of os.ModeAppend when writing patch files.