feat(child_process): make `kill` a function instead of a "method"

src/child_process_ffi.mjs

···
 
 export const spawn = (cmd, args) =>
   child_process.spawn(cmd, args.toArray())
+
+export const kill = (childProcess) =>
+  childProcess.kill()

src/plinth/node/child_process.gleam

···
 pub type ChildProcess {
-  ChildProcess(kill: fn() -> Nil, stdin: Stdin)
+  ChildProcess(stdin: Stdin)
 }
 
 pub type Stdin {
···
 
 @external(javascript, "../../child_process_ffi.mjs", "spawn")
 pub fn spawn(command: String, arguments: List(String)) -> ChildProcess
+
+@external(javascript, "../../child_process_ffi.mjs", "kill")
+pub fn kill(child_process: ChildProcess) -> Nil