Adopt AsyncAlgorithms (#167)

# Motivation

Now that `swift-async-algorithms` has a `1.0.0` tag we can depend on it instead of shipping our own version of `merge`.

Package.swift

@@ -34,7 +34,7 @@ let package = Package(
             from: "1.0.0"
         ),
         .package(
-            url: "https://github.com/apple/swift-collections.git",
+            url: "https://github.com/apple/swift-async-algorithms.git",
             from: "1.0.0"
         ),
     ],
@@ -46,7 +46,10 @@ let package = Package(
                     name: "Logging",
                     package: "swift-log"
                 ),
-                .target(name: "_AsyncMergeSequence"),
+                .product(
+                    name: "AsyncAlgorithms",
+                    package: "swift-async-algorithms"
+                ),
                 .target(name: "UnixSignals"),
                 .target(name: "ConcurrencyHelpers"),
             ]
@@ -66,15 +69,6 @@ let package = Package(
         .target(
             name: "ConcurrencyHelpers"
         ),
-        .target(
-            name: "_AsyncMergeSequence",
-            dependencies: [
-                .product(
-                    name: "DequeModule",
-                    package: "swift-collections"
-                ),
-            ]
-        ),
         .testTarget(
             name: "ServiceLifecycleTests",
             dependencies: [

Sources/ServiceLifecycle/AsyncCancelOnGracefulShutdownSequence.swift

@@ -12,7 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import _AsyncMergeSequence
+import AsyncAlgorithms
 
 extension AsyncSequence where Self: Sendable, Element: Sendable {
     /// Creates an asynchronous sequence that is cancelled once graceful shutdown has triggered.
@@ -44,7 +44,7 @@ public struct AsyncCancelOnGracefulShutdownSequence<Base: AsyncSequence & Sendab
 
     @inlinable
     public init(base: Base) {
-        self._merge = .init(
+        self._merge = merge(
             base.mapNil().map { .base($0) },
             AsyncGracefulShutdownSequence().mapNil().map { _ in .gracefulShutdown }
         )