cookie(
getenv,read) ->cookie
Read the client's cookie
getenv reads a variable, os.getenv by default; read reads a file,
std.fs.read_file by default. The first of $PULSE_COOKIE,
pulse/cookie under $XDG_CONFIG_HOME (else $HOME/.config), and
$HOME/.pulse-cookie that holds 256 bytes, libpulse's order. Returns nil
when none does. The device then sends zeros: a server takes a client of
its own uid by the socket's credentials, and pipewire-pulse never reads
the cookie.