fix: Stop using api_core default timeouts in publish since they are broken

[mukund-ananthu]

Change in behavior

60s initial deadline for RPCs reduced to 5s. Other timeout parameters changed changed:

ExponentialTimeout(
        initial=5, maximum=60, multiplier=1.3, deadline=600
    )

Change

Only non-test / non sample(i.e functional) usage found for PublisherOptions.timeout is here:

python-pubsub/google/cloud/pubsub_v1/publisher/client.py

Lines 440 to 441 in f648f65

	if timeout is gapic_v1.method.DEFAULT: # if custom timeout not passed in
	timeout = self.publisher_options.timeout

This change in usage is intended.

Call stack:

python-pubsub/google/cloud/pubsub_v1/publisher/client.py

Line 299 in f648f65

timeout: "types.OptionalTimeout" = gapic_v1.method.DEFAULT,

invokes one of the sequencers(ordered or unordered)

python-pubsub/google/cloud/pubsub_v1/publisher/client.py

Lines 477 to 479 in f648f65

	future = sequencer.publish(
	wrapper=wrapper, retry=retry, timeout=timeout
	)

which then create a batch with this timeout

python-pubsub/google/cloud/pubsub_v1/publisher/_sequencer/ordered_sequencer.py

Lines 255 to 263 in f648f65

	return self._client._batch_class(
	client=self._client,
	topic=self._topic,
	settings=self._client.batch_settings,
	batch_done_callback=self._batch_done_callback,
	commit_when_full=False,
	commit_retry=commit_retry,
	commit_timeout=commit_timeout,
	)

which uses it when committing the batch / publishing the messages:

python-pubsub/google/cloud/pubsub_v1/publisher/_batch/thread.py

Lines 323 to 328 in f648f65

	response = self._client._gapic_publish(
	topic=self._topic,
	messages=[wrapper.message for wrapper in self._message_wrappers],
	retry=self._commit_retry,
	timeout=self._commit_timeout,
	)

and invokes gapic_publish:

python-pubsub/google/cloud/pubsub_v1/publisher/client.py

Lines 289 to 291 in f648f65

	def _gapic_publish(self, *args, **kwargs) -> "pubsub_types.PublishResponse":
	"""Call the GAPIC public API directly."""
	return super().publish(*args, **kwargs)

which then uses it in the RPC call:

python-pubsub/google/pubsub_v1/services/publisher/client.py

Lines 1067 to 1072 in f648f65

	response = rpc(
	request,
	retry=retry,
	timeout=timeout,
	metadata=metadata,
	)

that is obtained by wrapping the transport base publish call:

python-pubsub/google/pubsub_v1/services/publisher/client.py

Line 1055 in f648f65

rpc = self._transport._wrapped_methods[self._transport.publish]

The wrapper uses the timeout when invoking the GapicCallable:

https://github.com/googleapis/python-api-core/blob/b1fae31c8c71ed65ad22a415dab2b54720c3d4ba/google/api_core/gapic_v1/method.py#L245-L252

which currently overrides float and int timeouts to use TimeToDeadlineTimeout:

https://github.com/googleapis/python-api-core/blob/b1fae31c8c71ed65ad22a415dab2b54720c3d4ba/google/api_core/gapic_v1/method.py#L112-L113

which is incorrect(why its incorrect is mentioned in the attached bug)

Fixes #1325 🦕

[mukund-ananthu]

@beltran PTAL