Scene storage backend integration (#51)

This PR adds Storyteller.ai API integration for saving and loading
Storyteller Studio scenes to/from the backend.

### Known issues
* The skybox is not currently stored in the serialized scene format

.github/workflows/pr-validation.yml

@@ -15,7 +15,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@1.76.0
+        with:
+          components: rustfmt
       - name: Check Rust formatting
         run: cargo fmt --all -- --check
 
@@ -35,7 +37,9 @@ jobs:
             ~/.cargo/git/db/
             target/
           key: ${{ runner.os }}-cargo-lint-and-test-${{ hashFiles('**/Cargo.toml') }}
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@1.76
+        with:
+          components: clippy
       - name: Install Linux dependencies
         run: |
               sudo apt-get update