Raw-string pexpect patterns to kill `SyntaxWarning`s

`tests.devx.test_tooling`'s end-of-tree `expect()` patterns use
a literal `\(` (pexpect regex), which Python 3.12+ flags as an
invalid escape sequence. Make them raw strings so the `\(` is
preserved verbatim and no `SyntaxWarning` fires.

(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

tests/devx/test_tooling.py

@@ -92,7 +92,7 @@ def test_shield_pause(
     expect(
         child,
         # end-of-tree delimiter
-        "end-of-\('root'",
+        r"end-of-\('root'",
     )
     _before: str = assert_before(
         child,
@@ -157,7 +157,7 @@ def test_shield_pause(
             expect(
                 child,
                 # end-of-subactor's-tree delimiter
-                "end-of-\('hanger'",
+                r"end-of-\('hanger'",
             )
             _before: str = assert_before(
                 child,