Add open-source 'basic' cache provider and revamp licensing documentation (#930)

## Summary

- **New `basic` cache provider**: Adds an open-source (MIT-licensed)
caching implementation built on `@actions/cache` as an alternative to
the proprietary Enhanced Caching. Users can opt in with `cache-provider:
basic` on both `setup-gradle` and `dependency-submission` actions.
- **Revamped licensing & distribution docs**: Replaces the verbose
licensing notice block (previously shown in README, docs, and logs) with
a friendlier callout and a new dedicated
[DISTRIBUTION.md](./DISTRIBUTION.md) covering component licensing, usage
tiers, data privacy ("Safe Harbor"), and opt-out instructions.
- **Improved messaging**: Enhanced Caching and Basic Caching each
display concise, informative log messages and job summary notes instead
of the previous wall-of-text license warning.
- **New integration tests**: Adds `integ-test-basic-cache-provider.yml`
workflow that seeds and verifies the basic cache provider across
platforms, plus unit tests for `BasicCacheService` and `getCacheService`
selection logic.
- **CI workflow reorganization**: Dependency-submission integration
tests extracted into their own reusable suite
(`suite-integ-test-dependency-submission.yml`); sample project tests
moved into the caching suite.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/integ-test-basic-cache-provider.yml

@@ -0,0 +1,67 @@
+name: Test basic cache provider
+
+on:
+  workflow_call:
+    inputs:
+      cache-key-prefix:
+        type: string
+        default: '0'
+      runner-os:
+        type: string
+        default: '["ubuntu-latest"]'
+      skip-dist:
+        type: boolean
+        default: false
+
+env:
+  SKIP_DIST: ${{ inputs.skip-dist }}
+  GRADLE_BUILD_ACTION_CACHE_KEY_PREFIX: basic-cache-provider-${{ inputs.cache-key-prefix }}
+
+permissions:
+  contents: read
+
+jobs:
+  basic-cache-seed-build:
+    strategy:
+      max-parallel: 1
+      fail-fast: false
+      matrix:
+        os: ${{fromJSON(inputs.runner-os)}}
+    runs-on: ${{ matrix.os }}
+    steps:
+    - name: Checkout sources
+      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+    - name: Initialize integ-test
+      uses: ./.github/actions/init-integ-test
+
+    - name: Setup Gradle with basic cache provider
+      uses: ./setup-gradle
+      with:
+        cache-provider: basic
+        cache-read-only: false # For testing, allow writing cache entries on non-default branches
+    - name: Build kotlin-dsl project
+      working-directory: .github/workflow-samples/kotlin-dsl
+      run: ./gradlew build
+
+  basic-cache-verify-build:
+    needs: basic-cache-seed-build
+    strategy:
+      max-parallel: 1
+      fail-fast: false
+      matrix:
+        os: ${{fromJSON(inputs.runner-os)}}
+    runs-on: ${{ matrix.os }}
+    steps:
+    - name: Checkout sources
+      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+    - name: Initialize integ-test
+      uses: ./.github/actions/init-integ-test
+
+    - name: Setup Gradle with basic cache provider
+      uses: ./setup-gradle
+      with:
+        cache-provider: basic
+        cache-read-only: true
+    - name: Build kotlin-dsl project
+      working-directory: .github/workflow-samples/kotlin-dsl
+      run: ./gradlew build --offline