📝 Add docs recommending Union over Optional and migrate source examples (#4908)

* 📝 Add docs recommending Union over Optional

* 📝 Update docs recommending Union over Optional

* 📝 Update source examples for docs, recommend Union over Optional

* 📝 Update highlighted lines with updated source examples

* 📝 Update highlighted lines in Markdown with recent code changes

* 📝 Update docs, use Union instead of Optional

* ♻️ Update source examples to recommend Union over Optional

* 🎨 Update highlighted code in Markdown after moving from Optional to Union

docs/zh/docs/tutorial/path-params-numeric-validations.md

@@ -43,7 +43,7 @@
 
 因此，你可以将函数声明为：
 
-```Python hl_lines="8"
+```Python hl_lines="7"
 {!../../../docs_src/path_params_numeric_validations/tutorial002.py!}
 ```
 
@@ -55,7 +55,7 @@
 
 Python 不会对该 `*` 做任何事情，但是它将知道之后的所有参数都应作为关键字参数（键值对），也被称为 <abbr title="来自：K-ey W-ord Arg-uments"><code>kwargs</code></abbr>，来调用。即使它们没有默认值。
 
-```Python hl_lines="8"
+```Python hl_lines="7"
 {!../../../docs_src/path_params_numeric_validations/tutorial003.py!}
 ```