fix(lsp): restore explicit _process cleanup in OSError handler

PR branch HEAD was using try-except-pass around stop() without an
explicit self._process = None assignment in the OSError exception
handler.  This corrected it to match master and the FileNotFoundError
pattern: direct stop() followed by explicit _process = None.

Closes #10597

src/cleveragents/lsp/transport.py

@@ -128,10 +128,8 @@ class StdioTransport:
             # raised (e.g. exec in a child fails), so we must terminate
             # and wait to avoid leaking a zombie or orphan.
             if self._process is not None:
-                try:
+                self.stop()
-                    self.stop()
+                self._process = None
-                except Exception:  # noqa: BLE001 -- best-effort cleanup
-                    pass
 
             from cleveragents.lsp.errors import LspError