Fix Ruby 4.0 warning in default before_template and after_template (#986)

Fixes #985

`SGML#call` passes the caller's block to `before_template` and
`after_template` via `&block`, but the default no-op implementations had
no block parameter. Ruby 4.0 warns about this:
```
warning: the block passed to 'before_template' may be ignored
warning: the block passed to 'after_template' may be ignored
```
I added `(&)` to both signatures so they accept the block without
binding it to a variable. Subclasses that override these methods won't
be affected.

Author: joeldrapper

lib/phlex/sgml.rb

@@ -326,11 +326,11 @@ def json_escape(string)
 		nil
 	end
 
-	private def before_template
+	private def before_template(&)
 		nil
 	end
 
-	private def after_template
+	private def after_template(&)
 		nil
 	end
 

quickdraw/sgml/callbacks.test.rb

@@ -30,4 +30,9 @@ def view_template
 	test "callbacks are called in the correct order" do
 		assert_equal Example.call, "<i>1</i><i>2</i><i>3</i><i>4</i><i>5</i><i>6</i><i>7</i>"
 	end
+
+	test "default before_template and after_template accept a block" do
+		klass = Class.new(Phlex::HTML) { def view_template = span { "hello" } }
+		assert_equal klass.call { "ignored" }, "<span>hello</span>"
+	end
 end