Improve Neovim 0.12+ health checks and local dev workflow

[Mathijs-Bakker]

Summary

This PR updates godotdev.nvim health reporting and documentation to better match modern Neovim setups, especially Neovim 0.12+ with built-in LSP and vim.pack.

It also fixes a few workflow issues uncovered while testing the plugin from a local development checkout.

Changes

• Treat built-in Neovim LSP as the baseline instead of warning about missing nvim-lspconfig
• Add formatter = false as an explicit opt-out for autoformat-on-save
• Update health checks to recognize newer nvim-treesitter module layouts
• Clean up :checkhealth godotdev output by removing duplicated status prefixes
• Add a DAP follow-up hint:
  nvim-dap is installed. Run :checkhealth dap for adapter-specific diagnostics.
• Update README and help docs for Neovim 0.12+:
  • remove nvim-lspconfig as a required dependency
  • add a vim.pack installation example
  • clarify that the plugin uses Neovim’s built-in LSP APIs
  • clarify that the plugin does not define LSP keymaps
• Add regression tests for:
  • formatter disabled behavior
  • built-in LSP health behavior
  • DAP health follow-up hint

Why

The plugin already uses Neovim’s core LSP APIs, so the old nvim-lspconfig health warning was misleading on valid 0.12+ setups.

While testing in a real vim.pack-based config, a stale installed plugin copy also made it clear that local development workflows and health messaging should be more explicit and less confusing.

Testing

• Ran nvim --headless -u NONE -c "luafile tests/run.lua" -c "qa!"
• All 27 tests passed