Conform client's tracing interceptor to OTel's conventions (#25)

This PR conforms the client tracing interceptor to follow
recommendations/conventions laid out in both:
- https://opentelemetry.io/docs/specs/semconv/rpc/rpc-spans
- https://opentelemetry.io/docs/specs/semconv/rpc/grpc/

Package.swift

@@ -47,7 +47,7 @@ let dependencies: [Package.Dependency] = [
   ),
   .package(
     url: "https://github.com/grpc/grpc-swift-protobuf.git",
-    exact: "1.0.0-beta.3"
+    branch: "main"
   ),
   .package(
     url: "https://github.com/apple/swift-protobuf.git",

Sources/GRPCInterceptors/HookedAsyncSequence.swift

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2025, gRPC Authors All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+internal struct HookedRPCAsyncSequence<Wrapped: AsyncSequence & Sendable>: AsyncSequence, Sendable
+where Wrapped.Element: Sendable {
+  private let wrapped: Wrapped
+
+  private let forEachElement: @Sendable (Wrapped.Element) -> Void
+  private let onFinish: @Sendable ((any Error)?) -> Void
+
+  init(
+    wrapping sequence: Wrapped,
+    forEachElement: @escaping @Sendable (Wrapped.Element) -> Void,
+    onFinish: @escaping @Sendable ((any Error)?) -> Void
+  ) {
+    self.wrapped = sequence
+    self.forEachElement = forEachElement
+    self.onFinish = onFinish
+  }
+
+  func makeAsyncIterator() -> HookedAsyncIterator {
+    HookedAsyncIterator(
+      self.wrapped,
+      forEachElement: self.forEachElement,
+      onFinish: self.onFinish
+    )
+  }
+
+  struct HookedAsyncIterator: AsyncIteratorProtocol {
+    typealias Element = Wrapped.Element
+
+    private var wrapped: Wrapped.AsyncIterator
+    private let forEachElement: @Sendable (Wrapped.Element) -> Void
+    private let onFinish: @Sendable ((any Error)?) -> Void
+
+    init(
+      _ sequence: Wrapped,
+      forEachElement: @escaping @Sendable (Wrapped.Element) -> Void,
+      onFinish: @escaping @Sendable ((any Error)?) -> Void
+    ) {
+      self.wrapped = sequence.makeAsyncIterator()
+      self.forEachElement = forEachElement
+      self.onFinish = onFinish
+    }
+
+    mutating func next(
+      isolation actor: isolated (any Actor)?
+    ) async throws(Wrapped.Failure) -> Wrapped.Element? {
+      do {
+        if let element = try await self.wrapped.next(isolation: actor) {
+          self.forEachElement(element)
+          return element
+        } else {
+          self.onFinish(nil)
+          return nil
+        }
+      } catch {
+        self.onFinish(error)
+        throw error
+      }
+    }
+
+    mutating func next() async throws -> Wrapped.Element? {
+      try await self.next(isolation: nil)
+    }
+  }
+}

Sources/GRPCInterceptors/HookedWriter.swift

@@ -18,27 +18,22 @@ internal import Tracing
 
 struct HookedWriter<Element: Sendable>: RPCWriterProtocol {
   private let writer: any RPCWriterProtocol<Element>
-  private let beforeEachWrite: @Sendable () -> Void
   private let afterEachWrite: @Sendable () -> Void
 
   init(
     wrapping other: some RPCWriterProtocol<Element>,
-    beforeEachWrite: @Sendable @escaping () -> Void,
     afterEachWrite: @Sendable @escaping () -> Void
   ) {
     self.writer = other
-    self.beforeEachWrite = beforeEachWrite
     self.afterEachWrite = afterEachWrite
   }
 
   func write(_ element: Element) async throws {
-    self.beforeEachWrite()
     try await self.writer.write(element)
     self.afterEachWrite()
   }
 
   func write(contentsOf elements: some Sequence<Element>) async throws {
-    self.beforeEachWrite()
     try await self.writer.write(contentsOf: elements)
     self.afterEachWrite()
   }