perf(lua): avoid spairs in vim.validate happy path

Problem:

`vim.validate` is too slow, mainly because of `vim.spairs`.

Solution:

Collect all errors in via `pairs`, and sort the errors via `spairs`.

runtime/lua/vim/shared.lua

@@ -796,16 +796,12 @@ do
     return type(val) == t or (t == 'callable' and vim.is_callable(val))
   end
 
-  --- @param opt table<vim.validate.Type,vim.validate.Spec>
+  --- @param param_name string
-  --- @return boolean, string?
+  --- @param spec vim.validate.Spec
-  local function is_valid(opt)
+  --- @return string?
-    if type(opt) ~= 'table' then
+  local function is_param_valid(param_name, spec)
-      return false, string.format('opt: expected table, got %s', type(opt))
-    end
-
-    for param_name, spec in vim.spairs(opt) do
     if type(spec) ~= 'table' then
-        return false, string.format('opt[%s]: expected table, got %s', param_name, type(spec))
+      return string.format('opt[%s]: expected table, got %s', param_name, type(spec))
     end
 
     local val = spec[1] -- Argument value
@@ -823,17 +819,17 @@ do
         local error_message =
           string.format('%s: expected %s, got %s', param_name, (spec[3] or '?'), tostring(val))
         if optional_message ~= nil then
-            error_message = error_message .. string.format('. Info: %s', optional_message)
+          error_message = string.format('%s. Info: %s', error_message, optional_message)
         end
 
-          return false, error_message
+        return error_message
       end
     elseif type(types) == 'table' then
       local success = false
       for i, t in ipairs(types) do
         local t_name = type_names[t]
         if not t_name then
-            return false, string.format('invalid type name: %s', t)
+          return string.format('invalid type name: %s', t)
         end
         types[i] = t_name
 
@@ -843,8 +839,7 @@ do
         end
       end
       if not success then
-          return false,
+        return string.format(
-            string.format(
           '%s: expected %s, got %s',
           param_name,
           table.concat(types, '|'),
@@ -852,7 +847,30 @@ do
         )
       end
     else
-        return false, string.format('invalid type name: %s', tostring(types))
+      return string.format('invalid type name: %s', tostring(types))
+    end
+  end
+
+  --- @param opt table<vim.validate.Type,vim.validate.Spec>
+  --- @return boolean, string?
+  local function is_valid(opt)
+    if type(opt) ~= 'table' then
+      return false, string.format('opt: expected table, got %s', type(opt))
+    end
+
+    local report --- @type table<string,string>?
+
+    for param_name, spec in pairs(opt) do
+      local msg = is_param_valid(param_name, spec)
+      if msg then
+        report = report or {}
+        report[param_name] = msg
+      end
+    end
+
+    if report then
+      for _, msg in vim.spairs(report) do -- luacheck: ignore
+        return false, msg
       end
     end