fix: contracts auto-deploy GitHub Actions workflow

[raulk]

This fixes our GitHub Actions workflow to auto-deploy contracts to Calibnet when changes are detected. This has been failing for some months and we never got around to fixing it. New users kept tripping up regularly when following the quickstart tutorial @ docs.ipc.space, which instructs them to deploy their subnet against the existing framework contracts on Calibnet. However, those contracts were outdated leading to severe compatibility issues.

While fixing this, I also:

• Simplified the setup by removing the need for a PAT.
• Removed the merge from main, as GH rejected pushes containing modified workflow files.
• Introduce a cache for incremental compilation and deployment (leveraging hardhat-deploy's ability to skip deployment when a contract with the same bytecode already exists).
• Eliminate random env variables carrying addresses and stdout parsing; instead just read the addresses from the deployment output files and generate a JSON file.