Ensure all imports of other modules are implementation only (#232)

Author: phausler

Sources/AsyncAlgorithms/AsyncChannel.swift

@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-@preconcurrency import OrderedCollections
+@preconcurrency @_implementationOnly import OrderedCollections
 
 /// A channel for sending elements from one task to another with back pressure.
 ///

Sources/AsyncAlgorithms/AsyncThrowingChannel.swift

@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-@preconcurrency import OrderedCollections
+@preconcurrency @_implementationOnly import OrderedCollections
 
 /// An error-throwing channel for sending elements from on task to another with back pressure.
 ///

Sources/AsyncAlgorithms/CombineLatest/CombineLatestStateMachine.swift

@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import DequeModule
+@_implementationOnly import DequeModule
 
 /// State machine for combine latest
 struct CombineLatestStateMachine<

Sources/AsyncAlgorithms/Merge/AsyncMerge2Sequence.swift

@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import DequeModule
+@_implementationOnly import DequeModule
 
 /// Creates an asynchronous sequence of elements from two underlying asynchronous sequences
 public func merge<Base1: AsyncSequence, Base2: AsyncSequence>(_ base1: Base1, _ base2: Base2) -> AsyncMerge2Sequence<Base1, Base2>

Sources/AsyncAlgorithms/Merge/AsyncMerge3Sequence.swift

@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import DequeModule
+@_implementationOnly import DequeModule
 
 /// Creates an asynchronous sequence of elements from two underlying asynchronous sequences
 public func merge<

Sources/AsyncAlgorithms/Merge/MergeStateMachine.swift

@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import DequeModule
+@_implementationOnly import DequeModule
 
 /// The state machine for any of the `merge` operator.
 ///