Refactor Neovim Configuration

[rikuson]

This commit implements several refactoring improvements to the Neovim configuration:

1. Create constants module (lua/config/constants.lua)

   • Centralize all magic numbers (timer intervals, file size limits, priorities)
   • Make configuration values easy to find and modify
   • Self-documenting with descriptive names

2. Fix easymotion timer memory leak

   • Replace recursive timer creation with single timer instance
   • Add proper timer cleanup on VimLeave
   • Use vim.uv instead of deprecated vim.loop
   • Remove global state dependency

3. Eliminate global function pollution (toggleterm.lua)

   • Replace global _lazygit_toggle() and _lazydocker_toggle() functions
   • Use local module pattern with lazy initialization
   • Improve encapsulation and testability

4. Consolidate duplicate Mason setup

   • Create dedicated mason.lua plugin file
   • Remove duplicate mason.setup() calls from nvim-lspconfig and none-ls
   • Prevent initialization race conditions
   • Use explicit dependencies

5. Add comprehensive error handling

   • Create utility module (lua/config/utils.lua) with safe_require and safe_execute
   • Add error handling to mason, nvim-lspconfig, and none-ls plugins
   • Provide clear error notifications on failure
   • Graceful degradation when plugins fail to load

All changes are non-breaking and maintain existing functionality while improving:

• Code maintainability
• Error resilience
• Performance (no timer leaks)
• Code organization