Opens a socket or named pipe at {address} and listens for |RPC| messages. Clients can send |API| commands to the returned address to control Nvim. Returns the address string (may differ from the requested {address}).

• If {address} contains a colon ":" it is interpreted as a TCP/IPv4/IPv6 address where the last ":" separates host and port (empty or zero assigns a random port).
• Else it is interpreted as a named pipe or Unix domain socket path. If there are no slashes it is treated as a name and appended to a generated path.
• If {address} is empty it generates a path. Example named pipe: if has('win32') echo serverstart('\.\pipe\nvim-pipe-1234') else echo serverstart('nvim.sock') endif Example TCP/IP address: echo serverstart('::1:12345')