refactor(nvim): update conform formatters and enable format-on-save

Reorder rust formatters (rustfmt primary), switch python from
isort/black to ruff/dprint, and enable format_on_save with lsp_fallback.

config/nvim/plugin/conform.lua

@@ -21,8 +21,8 @@ conform.setup({
         cpp = { "clang_format" },
         lua = { 'stylua' },
         go = { "goimports", "gofmt" },
-        rust = { "dprint", "rustfmt", lsp_format = "fallback" },
-        python = { "isort", "black", stop_after_first = true },
+        rust = { "rustfmt", "dprint", lsp_format = "fallback" },
+        python = { "ruff", "dprint", stop_after_first = true },
         javascript = { "dprint", "prettier", stop_after_first = true },
         markdown = { "dprint", "prettier", stop_after_first = true },
         javascriptreact = { "dprint", "prettier", stop_after_first = true },
@@ -31,12 +31,13 @@ conform.setup({
         svelte = { "dprint", "prettier", stop_after_first = true },
         html = { "dprint", "prettier", stop_after_first = true },
     },
+    format_on_save = {
+        lsp_fallback = true,
+    },
 })
 
 vim.keymap.set({ 'n', 'v' }, '<leader>bf',
     function()
-    conform.format { async = true, lsp_format = 'fallback' }
+        conform.format { async = true }
     end,
     { desc = 'Format buffer' })
-
-