fix: add cryptography to pyproject.toml dependencies

muxplex/tls.py imports cryptography for self-signed cert generation
but it was missing from the declared dependencies. uv tool installs
would fail with ModuleNotFoundError on setup-tls.

pyproject.toml

@@ -19,6 +19,7 @@ dependencies = [
     "itsdangerous>=2.1.0",
     "python-multipart>=0.0.9",
     "httpx>=0.27.0",
+    "cryptography",
 ]
 
 [project.optional-dependencies]