Copilot: Update instructions, place NDK in /tmp

IS_COPILOT=true isn't persistent, so copilot is instructed to set this var for every gradle build on the command line itself by the "copilot-instructions.md" file.

.github/copilot-instructions.md

@@ -1,12 +1,14 @@
 ## Copilot Coding Agent Configuration
 
-If running in coding agent (padawan) mode on GitHub, make sure to use the
-`report_progress` tool to push commits to the remote repository. Do not attempt
-to use git push as you do not have write access to the repository directly.
-
 We use Java 21 (eclipse-temurin:21-jdk-jammy) to build the app via gradle.
 
-Only use the "debug" flavor of the app when you make builds.
-You cannot build "release" as the signing keys are not part of the repository.
+If you do gradle tasks, you need to prefix them by the following env var to decrease build time. If you forget to set the env var "IS_COPILOT" to "true", the gradle buildNative task will execute which is not required for your work.
+```bash
+IS_COPILOT=true
+```
+Example: "IS_COPILOT=true gradle assembleDebug"
+
+Only use the "debug" flavor of the app when you make gradle builds.
+You cannot gradle build "release" as the signing keys are not part of the repository.
 
 Do not try to upgrade the kotlin version in "gradle/libs.versions.toml", it will throw a lot of warnings and errors.

.github/workflows/copilot-setup-steps.yml

@@ -18,7 +18,7 @@ jobs:
       contents: read
 
     env:
-      IS_COPILOT: true
+      COPILOT_BUILDTOOLS_DIR: /tmp/copilot-build-tools
 
     steps:
       - name: Checkout code including submodules
@@ -49,10 +49,10 @@ jobs:
           ANDROID_NDK_VERSION=r28
           ANDROID_NDK_ZIP="android-ndk-${ANDROID_NDK_VERSION}-linux.zip"
           ANDROID_NDK_URL="https://dl.google.com/android/repository/${ANDROID_NDK_ZIP}"
-          wget -q "$ANDROID_NDK_URL"
-          unzip -q "$ANDROID_NDK_ZIP" -d $HOME
-          echo "ANDROID_NDK_HOME=$HOME/android-ndk-${ANDROID_NDK_VERSION}" >> $GITHUB_ENV
-          echo "$HOME/android-ndk-${ANDROID_NDK_VERSION}" >> $GITHUB_PATH
+          mkdir -p "$COPILOT_BUILDTOOLS_DIR"
+          wget -q "$ANDROID_NDK_URL" -O "$COPILOT_BUILDTOOLS_DIR/$ANDROID_NDK_ZIP"
+          unzip -q "$COPILOT_BUILDTOOLS_DIR/$ANDROID_NDK_ZIP" -d "$COPILOT_BUILDTOOLS_DIR"
+          echo "ANDROID_NDK_HOME=$COPILOT_BUILDTOOLS_DIR/android-ndk-${ANDROID_NDK_VERSION}" >> $GITHUB_ENV
 
       - name: Cache Gradle packages
         uses: actions/cache@v3