fix: TLSSession guards unbuilt session in _is_closed/close; document setup() is not auto-invoked

_is_closed() and close() called self.session unconditionally, routing through the
lazy session property and building a real backend client even when the session was
never used - including during __del__ on GC of a constructed-but-unused TLSSession,
silently building (and leaking) a backend client nothing ever closes. Mirrors
aioweb.ExtendedSession's own _session is None guards. Also corrects setup()'s
docstring, which claimed TLSSession invokes a backend's setup() lazily before the
first request - it never does; only Noble self-invokes it from its own raw_request.

Signed-off-by: disqualifier <dev@disqualifier.me>

src/aioweb_tls/session.py

@@ -38,8 +38,10 @@ class TLSSession(ExtendedSession):
     async def setup(self) -> None:
         """run the backend's one-time setup if it has one (idempotent, e.g. noble's Go lib fetch)
 
-        optional to call: also invoked lazily before the first request, but calling
+        optional to call upfront to pre-warm at startup. TLSSession itself never calls
-        it upfront lets callers pre-warm at startup.
+        this automatically - a backend needing lazy setup must self-invoke it from its
+        own raw_request, as Noble does; a custom backend that skips this will never run
+        setup() unless the caller calls TLSSession.setup() explicitly.
         """
         setup = getattr(self.backend, "setup", None)
         if setup is not None:
@@ -64,9 +66,14 @@ class TLSSession(ExtendedSession):
         return cookies_for_url(self.session, url)
 
     def _is_closed(self) -> bool:
-        """closed if explicitly closed here or the backend reports it"""
+        """closed if explicitly closed here, never built, or the backend reports it
+
+        an unbuilt session counts as closed: nothing was opened, nothing to leak.
+        """
         if self._closed:
             return True
+        if self._session is None:
+            return True
         return self.backend.is_closed(self.session)
 
     # -------------------------------------------------------------------------
@@ -104,10 +111,12 @@ class TLSSession(ExtendedSession):
     #   lifecycle - backends close differently, so route through the backend
 
     async def close(self) -> None:
-        """close via the backend's close (falls back to session.close)"""
+        """close via the backend's close (falls back to session.close); no-op if never built"""
         self._closed = True
+        if self._session is None:
+            return
         close = getattr(self.backend, "close", None)
         if close is not None:
-            await close(self.session)
+            await close(self._session)
         else:
-            await self.session.close()
+            await self._session.close()