ci: binary-compat API baselines, multiplatform matrix CI, module docs

- Commit binary-compatibility-validator .api baselines for core + both modules.
- Replace JVM-only CI with a matrix: Ubuntu runs JVM/JS(node)/Wasm(node)/Native
  + apiCheck; macOS runs the iOS simulator tests.
- README: install + usage for tree-structure-serialization and -coroutines.
- Update kotlin-js-store/yarn.lock for the new modules' JS test deps.

Verified locally: JVM, JS(node), Wasm(node) and iOS-simulator tests pass for
core + both modules; native compiles & links (exec runs on the Linux CI runner).

.github/workflows/test.yml

@@ -6,9 +6,19 @@ on:
   workflow_call:
 
 jobs:
-  build:
-    name: Run unit tests
-    runs-on: ubuntu-latest
+  test:
+    name: ${{ matrix.name }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - name: JVM / JS / Wasm / Native + API check
+            os: ubuntu-latest
+            tasks: jvmTest jsNodeTest wasmJsNodeTest nativeTest apiCheck
+          - name: iOS
+            os: macos-latest
+            tasks: iosSimulatorArm64Test
     steps:
       - name: Check out code
         uses: actions/checkout@v4
@@ -17,7 +27,5 @@ jobs:
         with:
           distribution: temurin
           java-version: '21'
-
-        # Builds the release artifacts of the library
       - name: Test
-        run: ./gradlew cleanJvmTest jvmTest
+        run: ./gradlew ${{ matrix.tasks }} --console=plain