Fix minor typechecking issues

These changes ought to be no-ops. There are a few spots where PyLance
flags inconsistent return types or the lack of a method definition and
this plugs those small holes.

Author: kgaughan

src/waitress/channel.py

@@ -85,7 +85,7 @@ def writable(self):
         # the channel (possibly by our server maintenance logic), run
         # handle_write
 
-        return self.total_outbufs_len or self.will_close or self.close_when_flushed
+        return self.total_outbufs_len > 0 or self.will_close or self.close_when_flushed
 
     def handle_write(self):
         # Precondition: there's data in the out buffer to be sent, or
@@ -135,6 +135,8 @@ def _flush_exception(self, flush, do_close=True):
 
                 return (False, True)
 
+        return (False, False)
+
     def readable(self):
         # We might want to read more requests. We can only do this if:
         # 1. We're not already about to close the connection.

src/waitress/task.py

@@ -295,6 +295,9 @@ def remove_content_length_header(self):
     def start(self):
         self.start_time = time.time()
 
+    def execute(self):
+        raise NotImplementedError  # pragma: no cover
+
     def finish(self):
         if not self.wrote_header:
             self.write(b"")

src/waitress/wasyncore.py

@@ -328,7 +328,7 @@ def del_channel(self, map=None):
     def create_socket(self, family=socket.AF_INET, type=socket.SOCK_STREAM):
         self.family_and_type = family, type
         sock = socket.socket(family, type)
-        sock.setblocking(0)
+        sock.setblocking(False)
         self.set_socket(sock)
 
     def set_socket(self, sock, map=None):
@@ -353,10 +353,10 @@ def set_reuse_addr(self):
     # to pass to select().
     # ==================================================
 
-    def readable(self):
+    def readable(self) -> bool:
         return True
 
-    def writable(self):
+    def writable(self) -> bool:
         return True
 
     # ==================================================