Wrap rd_kafka_consumer_poll into iterator (use librdkafka embedded backpressure) (#158)

* remove message sequence

* test consumer with implicit rebalance

* misc + format

* remove artefact

* don't check a lot of messages

* fix typo

* slow down first consumer to lower message to fit CI timeout

* remove helpers

* use exact benchmark version to avoid missing thresholds error (as no thresholds so far)

* add deprecated marks for backpressure, change comment for future dev

* address comments

Author: blindspotbounty

Sources/Kafka/Configuration/KafkaConsumerConfiguration.swift

@@ -12,7 +12,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-import Crdkafka
 import struct Foundation.UUID
 
 public struct KafkaConsumerConfiguration {
@@ -23,37 +22,6 @@ public struct KafkaConsumerConfiguration {
     /// Default: `.milliseconds(100)`
     public var pollInterval: Duration = .milliseconds(100)
 
-    /// A struct representing different back pressure strategies for consuming messages in ``KafkaConsumer``.
-    public struct BackPressureStrategy: Sendable, Hashable {
-        enum _BackPressureStrategy: Sendable, Hashable {
-            case watermark(low: Int, high: Int)
-        }
-
-        let _internal: _BackPressureStrategy
-
-        private init(backPressureStrategy: _BackPressureStrategy) {
-            self._internal = backPressureStrategy
-        }
-
-        /// A back pressure strategy based on high and low watermarks.
-        ///
-        /// The consumer maintains a buffer size between a low watermark and a high watermark
-        /// to control the flow of incoming messages.
-        ///
-        /// - Parameter low: The lower threshold for the buffer size (low watermark).
-        /// - Parameter high: The upper threshold for the buffer size (high watermark).
-        public static func watermark(low: Int, high: Int) -> BackPressureStrategy {
-            return .init(backPressureStrategy: .watermark(low: low, high: high))
-        }
-    }
-
-    /// The backpressure strategy to be used for message consumption.
-    /// See ``KafkaConsumerConfiguration/BackPressureStrategy-swift.struct`` for more information.
-    public var backPressureStrategy: BackPressureStrategy = .watermark(
-        low: 10,
-        high: 50
-    )
-
     /// A struct representing the different Kafka message consumption strategies.
     public struct ConsumptionStrategy: Sendable, Hashable {
         enum _ConsumptionStrategy: Sendable, Hashable {