docs: add notes for datetime ms/us in model and query builder

Author: kenjis

user_guide_src/source/models/model.rst

@@ -395,6 +395,18 @@ The datetime format is set in the ``dateFormat`` array of the
 :ref:`database configuration <database-config-explanation-of-values>` in the
 **app/Config/Database.php** file.
 
+.. note::
+    When you set ``ms`` or ``us`` as a parameter, **Model** takes care of second's
+    fractional part of the Time. But **Query Builder** does not. So you still need
+    to use the ``format()`` method when you pass the Time to Query Builder's methods
+    like ``where()``:
+
+    .. literalinclude:: model/063.php
+        :lines: 2-
+
+.. note:: Prior to v4.6.0, you cannot use ``ms`` or ``us`` as a parameter.
+    Because the second's fractional part of Time was lost due to bugs.
+
 Custom Casting
 ==============
 

user_guide_src/source/models/model/063.php

@@ -0,0 +1,13 @@
+<?php
+
+$model = model('SomeModel');
+
+$now = \CodeIgniter\I18n\Time::now();
+
+// The following code passes the microseconds to Query Builder.
+$model->where('my_dt_field', $now->format('Y-m-d H:i:s.u'))->findAll();
+// Generates: SELECT * FROM `my_table` WHERE `my_dt_field` = '2024-07-28 18:57:58.900326'
+
+// But the following code loses the microseconds.
+$model->where('my_dt_field', $now)->findAll();
+// Generates: SELECT * FROM `my_table` WHERE `my_dt_field` = '2024-07-28 18:57:58'