Confluent kafka Producer doesn't return expected values from poll() and flush() methods when instrumented by ConfluentKafkaInstrumentor().instrument_producer()

[dferrochio]

Describe your environment

python 3.9
confluent-kafka==2.3.0
opentelemetry-instrumentation-confluent-kafka==0.45b0
opentelemetry-semantic-conventions==0.45b0

Steps to reproduce
Spin up a kafka broker:

docker run -d --name kafka-server --hostname kafka-server \
    -e KAFKA_CFG_NODE_ID=0 \
    -e KAFKA_CFG_PROCESS_ROLES=controller,broker \
    -e KAFKA_CFG_LISTENERS=PLAINTEXT://:9092,CONTROLLER://:9093 \
    -e KAFKA_CFG_LISTENER_SECURITY_PROTOCOL_MAP=CONTROLLER:PLAINTEXT,PLAINTEXT:PLAINTEXT \
    -e KAFKA_CFG_CONTROLLER_QUORUM_VOTERS=0@kafka-server:9093 \
    -e KAFKA_CFG_CONTROLLER_LISTENER_NAMES=CONTROLLER \
    bitnami/kafka:latest

Run this code:

from opentelemetry.instrumentation.confluent_kafka import ConfluentKafkaInstrumentor
from confluent_kafka import Producer

inst = ConfluentKafkaInstrumentor()
p = confluent_kafka.Producer({'bootstrap.servers': 'localhost:9092'})
p = inst.instrument_producer(p)
p.produce('my-topic', b'raw_bytes')
msg = p.poll(0)
print(msg)
msg_pending = p.flush5)
print(msg_pending)

What is the expected behavior?
Should be printed:

0
1

Producer poll() and flush() methods should return integers.

What is the actual behavior?

None
None

Producer poll() and flush() methods are returning None

Additional context

flush and poll methods doesn't have a return statement:

opentelemetry-python-contrib/instrumentation/opentelemetry-instrumentation-confluent-kafka/src/opentelemetry/instrumentation/confluent_kafka/__init__.py

Line 154 in 460fc33

self._producer.flush(timeout)

opentelemetry-python-contrib/instrumentation/opentelemetry-instrumentation-confluent-kafka/src/opentelemetry/instrumentation/confluent_kafka/__init__.py

Line 157 in 460fc33

self._producer.poll(timeout)