refactor!: use OO & add tests (#100)

* I did an overhall for all codes and added typing by Lua-language-server and tests. It also works on CI.
* Now it searches files on the workspace completely asynchronously. It does not block your text input. (Fix #106)
Make count = 1 when you open a file you've never opened (Fix #107)

lua/telescope/_extensions/frecency.lua

@@ -1,29 +1,21 @@
-local telescope = (function()
-  local ok, m = pcall(require, "telescope")
-  if not ok then
-    error "telescope-frecency: couldn't find telescope.nvim, please install"
-  end
-  return m
-end)()
+local frecency = require "frecency"
 
-local picker = require "frecency.picker"
-
-return telescope.register_extension {
-  setup = picker.setup,
+return require("telescope").register_extension {
+  setup = frecency.setup,
   health = function()
-    if ({ pcall(require, "sqlite") })[1] then
-      vim.health.report_ok "sql.nvim installed."
+    if vim.F.npcall(require, "sqlite") then
+      vim.health.ok "sqlite.lua installed."
     else
-      vim.health.report_error "sql.nvim is required for telescope-frecency.nvim to work."
+      vim.health.error "sqlite.lua is required for telescope-frecency.nvim to work."
     end
-    if ({ pcall(require, "nvim-web-devicons") })[1] then
-      vim.health.report_ok "nvim-web-devicons installed."
+    if vim.F.npcall(require, "nvim-web-devicons") then
+      vim.health.ok "nvim-web-devicons installed."
     else
-      vim.health.report_info "nvim-web-devicons is not installed."
+      vim.health.info "nvim-web-devicons is not installed."
     end
   end,
   exports = {
-    frecency = picker.fd,
-    complete = picker.complete,
+    frecency = frecency.start,
+    complete = frecency.complete,
   },
 }