feat: add health checker

autoload/health/gopher.vim

···
+function! health#gopher#check()
+  lua require"gopher.health".check()
+endfunction

lua/gopher/_utils/init.lua

···
 
     return s:sub(1, n)
   end,
+
+  ---@param lib string
+  ---@return boolean
+  lualib_is_found = function(lib)
+    local is_found, _ = pcall(require, lib)
+    return is_found
+  end,
+
+  ---@param bin string
+  ---@return boolean
+  binary_is_found = function(bin)
+    if vim.fn.executable(bin) == 1 then
+      return true
+    end
+
+    return false
+  end,
 }

lua/gopher/health.lua

···
+local utils = require "gopher._utils"
+local M = {
+  _required = {
+    plugins = {
+      { lib = "plenary" },
+      { lib = "nvim-treesitter" },
+    },
+    binarys = {
+      { bin = "go", help = "required for GoMod command" },
+      { bin = "gomodifytags", help = "required for modify struct tags" },
+    },
+  },
+}
+
+function M.check()
+  vim.health.report_start "Required plugins"
+  for _, plugin in ipairs(M._required.plugins) do
+    if utils.lualib_is_found(plugin.lib) then
+      vim.health.report_ok(plugin.lib .. " installed.")
+    else
+      vim.health.report_error(plugin.lib .. " not found. Gopher.nvim will not work without it!")
+    end
+  end
+
+  vim.health.report_start "Required go tools"
+  for _, binary in ipairs(M._required.binarys) do
+    if utils.binary_is_found(binary.bin) then
+      vim.health.report_ok(binary.bin .. " installed")
+    else
+      vim.health.report_warn(binary.bin .. " is not installed but " .. binary.help)
+    end
+  end
+end
+
+return M