feat: add Rust build caching to ci-lazer-solana workflow

- Add cache-workspaces parameter to actions-rust-lang/setup-rust-toolchain@v1
- Cache target/ directory using Cargo.lock hash as cache key
- Follows same pattern as other lazer workflows in pyth-examples
- Improves build performance by caching compiled dependencies

Co-Authored-By: Jayant <[email protected]>

Author: devin-ai-integration[bot]

.github/workflows/ci-lazer-solana.yml

@@ -18,6 +18,7 @@ jobs:
         with:
           toolchain: 1.81.0
           components: clippy, rustfmt
+          cache-workspaces: "lazer/solana -> target"
       - name: install extra tools
         run: |
           cargo install --locked [email protected]