Save chats to lua

[e2r2fx]

Description

Saving chat history with tool calls resulted in several issues with encoding decoding. Storing to lua prevents the need from stripping functions and having to handle edge cases when storing.

Also using new ChatDone event makes sure chat is only saved a single time at the end of an interaction.

Tool output is hidden before saving to disk.

Related Issue(s)

• Fixes [ENH]: Option to hide tool output? #31
• Fixes fix: auto save not working #40

Checklist

• I've read the contributing guidelines and have adhered to them in this PR
• I've updated the README and/or relevant docs pages
• I've run make test to ensure all tests pass
• I've run make format to format the code
• I've run make docs to update the vimdoc pages

[e2r2fx]

@ravitemer I put a hold on this because I noticed the API in CC is changing and there's still some bugs to be squashed. I pinned my config to codecompanion v17.11.0 until the dust settles. With latest codecompanion and codecompanion-history I lost context (probably due to the new key).