Implement Pkl binary renderer and parser (#1203)

Implements a binary renderer for Pkl values, which is a lossless capturing of Pkl data.

This follows the pkl binary format that is already used with `pkl server` calls, and is
made available as a Java API and also an in-language API.

Also, introduces a binary parser into the corresponding `PObject` types in Java.

stdlib/pklbinary.pkl

@@ -0,0 +1,28 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the Pkl project 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
+//
+//     https://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.
+//===----------------------------------------------------------------------===//
+
+/// APIs for handling Pkl's [binary encoding format](https://pkl-lang.org/main/current/bindings-specification/binary-encoding.html).
+@ModuleInfo { minPklVersion = "0.30.0" }
+module pkl.pklbinary
+
+/// Render values as the [`pkl-binary` encoding format](https://pkl-lang.org/main/current/bindings-specification/binary-encoding.html).
+class Renderer extends BytesRenderer {
+  /// Render a Pkl value as `pkl-binary`.
+  external function renderValue(value: Any): Bytes
+
+  /// Render a Pkl document as `pkl-binary`.
+  external function renderDocument(value: Any): Bytes
+}