completely refactor and modularize flake

modules/default/common/nixvim/cmp.nix

@@ -0,0 +1,49 @@
+{ ... }:
+{
+
+  programs.nixvim.plugins = {
+    cmp = {
+      enable = true;
+      settings = {
+        autoEnableSources = true;
+        experimental = {ghost_text = false;};
+        performance = {
+          debounce = 60;
+          fetchingTimeout = 200;
+          maxViewEntries = 30;
+        };
+        snippet = {expand = "luasnip";};
+        formatting = {fields = ["kind" "abbr" "menu"];};
+        sources = [
+          {name = "git";}
+          {name = "nvim_lsp";}
+          {name = "emoji";}
+          {
+            name = "buffer"; # text within current buffer
+            option.get_bufnrs.__raw = "vim.api.nvim_list_bufs";
+            keywordLength = 3;
+          }
+          {
+            name = "path"; # file system paths
+            keywordLength = 3;
+          }
+          {
+            name = "luasnip"; # snippets
+            keywordLength = 3;
+          }
+        ];
+
+        window = {
+          completion = {border = "solid";};
+          documentation = {border = "solid";};
+        };
+      };
+    };
+    cmp-nvim-lsp = {enable = true;}; # lsp
+    cmp-buffer = {enable = true;};
+    cmp-path = {enable = true;}; # file system paths
+    cmp_luasnip = {enable = true;}; # snippets
+    cmp-cmdline = {enable = false;}; # autocomplete for cmdline
+  };
+
+}