Add pre_pty_read_hook in pty_read

[Wh1isper]

In jupyter server, last_activity is patched into ptywclients in handler

class TermSocket(WebSocketMixin, JupyterHandler, terminado.TermSocket):
    ...
    def _update_activity(self):
        self.application.settings["terminal_last_activity"] = utcnow()
        # terminal may not be around on deletion/cull
        if self.term_name in self.terminal_manager.terminals:
            self.terminal_manager.terminals[self.term_name].last_activity = utcnow()

If we close the browser or refresh it, these is no socket to update last_activity

Also if we execute some time consuming terminal(like below), last_activity will not be updated

$python
Python 3.8.12 (default, Dec 21 2021, 07:30:29) 
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import time
>>> while True:
...   time.sleep(1)
...   print(1)
... 

So this PR introduces pre_pty_read_hook, which allows the jupyter server's TerminalManager to update the pty when it is reading

in jupyter server (I will create a pr in jupyter server as well)

class TerminalManager(LoggingConfigurable, terminado.NamedTermManager):
    def pre_pty_read_hook(self, ptywclients):
        ptywclients.last_activity = utcnow()