pins/codecompanion-nvim: bump to v18.3.0

[suicide]

updated codecompanion to the latest 18.3.0.

The update is necessary for compatibility with latest mcphub-nvim, see also #1173. Without it codecompanion cannot properly show mcphub tools/vars/commands

Sanity Checking

• I have updated the changelog as per my changes
• I have tested, and self-reviewed my code
• My changes fit guidelines found in hacking nvf
• Style and consistency
  • I ran Alejandra to format my code (nix fmt)
  • My code conforms to the editorconfig configuration of the project
  • My changes are consistent with the rest of the codebase
• If new changes are particularly complex:
  • My code includes comments in particularly complex areas
  • I have added a section in the manual
  • (For breaking changes) I have included a migration guide
• Package(s) built:
  • .#nix (default package)
  • .#maximal
  • .#docs-html (manual, must build)
  • .#docs-linkcheck (optional, please build if adding links)
• Tested on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin

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[NotAShelf]

Thank you :)

Fyi we don't actually use conventional commits, but instead we use scoped commits as described in the hacking guidelines. It's obviously not a blocker, but it helps avoid squash merges.