This PR addresses the changes requested in #346 from earlier this year, as I also would like to be able to use this feature.

It adds 2 new outputs: CACHE-HIT and PUB-CACHE-HIT. These just pass along the cache-hit output from actions/cache@v4 for the cache-flutter and cache-pub steps. These can be used for increasing workflow efficiency through steps like conditionally installing dependencies when the cache is invalid. The README is also updated with example usage to skip melos bootstrap if PUB-CACHE-HIT was not true.

I tested the outputs here: https://github.com/beninato8-forks/flutter-action/actions/runs/15627281250/job/44023816175

Cache restored successfully
Cache restored from key: flutter-linux-stable-3.27.4-x64-d8a9f9a52e5af486f80d932e838ee93861ffd863
...
Cache restored successfully
Cache restored from key: flutter-pub-linux-stable-3.27.4-x64-d8a9f9a52e5af486f80d932e838ee93861ffd863-
...
Cache Hit: true
Pub Cache Hit: true

Output from the following steps (after a previous run was cached):

- name: Flutter Action 1
  uses: ./
  id: flutter-action-1
  with:
    flutter-version: '3.27.x'
    channel: 'stable'
    cache: true

- name: Print Action Outputs 1
  run: |
    echo "Cache Hit: ${{ steps.flutter-action-1.outputs.CACHE-HIT }}"
    echo "Pub Cache Hit: ${{ steps.flutter-action-1.outputs.PUB-CACHE-HIT }}"

This PR closes #346