py(deps): Add textframe extras with syrupy dependency

why: Allow opt-in installation of textframe pytest plugin.
what:
- Add [project.optional-dependencies] textframe = ["syrupy>=4.0.0"]
- Add [project.entry-points.pytest11] libtmux-textframe entry point
- Downstream users can now: pip install libtmux[textframe]

Author: tony

pyproject.toml

@@ -113,8 +113,12 @@ lint = [
   "mypy",
 ]
 
+[project.optional-dependencies]
+textframe = ["syrupy>=4.0.0"]
+
 [project.entry-points.pytest11]
 libtmux = "libtmux.pytest_plugin"
+libtmux-textframe = "libtmux.textframe.plugin"
 
 [build-system]
 requires = ["hatchling"]