Refactor encoder property to weak reference in KeyedContainerImpl and UnkeyedContainerImpl to prevent retain cycles

Sources/Leaf/LeafEncoder.swift

@@ -151,7 +151,7 @@ extension LeafEncoder {
     }
 
     private final class KeyedContainerImpl<Key>: KeyedEncodingContainerProtocol, LeafEncodingResolvable where Key: CodingKey {
-        private let encoder: EncoderImpl
+        private unowned let encoder: EncoderImpl
         private var data: [String: any LeafEncodingResolvable] = [:]
         private var nestedEncoderCaptures: [AnyObject] = []
 
@@ -230,7 +230,7 @@ extension LeafEncoder {
     }
 
     private final class UnkeyedContainerImpl: UnkeyedEncodingContainer, LeafEncodingResolvable {
-        private let encoder: EncoderImpl
+        private unowned let encoder: EncoderImpl
         private var data: [any LeafEncodingResolvable] = []
         private var nestedEncoderCaptures: [AnyObject] = []
 

Tests/LeafTests/LeafMemoryGrowthTests.swift

@@ -0,0 +1,50 @@
+import XCTest
+import Leaf
+import LeafKit
+import XCTVapor
+
+/*
+ to profile memory growth, use an sh script like this:
+ ```bash
+ #!/bin/zsh
+ swift test --filter LeafMemoryGrowthTests &
+ sleep 5
+ PID=$(ps aux | grep '[l]eafPackageTests' | awk '{print $2}' | head -n1)
+ echo "leafPackageTests PID: $PID"
+ leaks $PID
+ ```
+*/
+final class LeafMemoryGrowthTests: XCTestCase {
+    func testRepeatedRenderMemoryGrowth() async throws {
+        sleep(3) // Keep process alive for leaks profiling
+        var test = TestFiles()
+        test.files["/foo.leaf"] = "Hello #(name)!"
+
+        try await withApp { app in
+            app.views.use(.leaf)
+            app.leaf.sources = .singleSource(test)
+            struct Foo: Encodable { var name: String }
+            // Render with context 1000 times
+            for _ in 0..<1000 {
+                _ = try await app.leaf.renderer.render(path: "foo", context: Foo(name: "World")).get()
+            }
+        }
+        sleep(10) // Keep process alive for leaks profiling
+    }
+
+    func testRepeatedRenderNoContextMemoryGrowth() async throws {
+        sleep(3) // Keep process alive for leaks profiling
+        var test = TestFiles()
+        test.files["/foo.leaf"] = "Hello!"
+
+        try await withApp { app in
+            app.views.use(.leaf)
+            app.leaf.sources = .singleSource(test)
+            // Render without context 1000 times (pass nil context)
+            for _ in 0..<1000 {
+                _ = try await app.leaf.renderer.render(path: "foo", context: Optional<Bool>.none).get()
+            }
+        }
+        sleep(10) // Keep process alive for leaks profiling
+    }
+}