fix: propagate read errors from getKeyPress instead of busy-looping

[ruslsalimov]

Fixes #15

getKeyPress turned every error from inputTTY.Read into an empty keys.Key{} with a nil error.
When the terminal goes away (window closed, SIGHUP not delivered or ignored), read on /dev/tty
returns EIO immediately and forever, so Listen spins at 100%+ CPU and never returns.
Measurements, debugger output and the commit history behind the swallowing are in the issue.

Changes

• getKeyPress returns the read error, as the original 2022-06-01 code did.
• Listen decides what a read error means: if stopRoutine is already set — stop() sets it
  before closing/cancelling the fd — the read was interrupted by our own stop (Close on Unix,
  CancelIoEx on Windows) and it is a normal shutdown; otherwise Listen restores the console
  (stop() + stopListener()) and returns the error.