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

[devin-ai-integration]

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

Summary

Adds Rust build caching to the ci-lazer-solana.yml GitHub Actions workflow by including the cache-workspaces parameter in the existing actions-rust-lang/setup-rust-toolchain@v1 step. This will cache the target/ directory using the Cargo.lock file hash as the cache key, improving build performance by avoiding recompilation of unchanged dependencies.

The implementation follows the same pattern used in other Rust workflows in this repository (ci-lazer-anchor.yml) and the broader pyth-network organization.

Review & Testing Checklist for Human

• Verify cache path correctness: Confirm that "lazer/solana -> target" correctly maps to the working directory lazer/solana and that Rust builds output to target/ in that directory
• Test CI pipeline: Run the workflow on this PR and verify all steps complete successfully with caching enabled
• Monitor performance improvement: On subsequent runs (after cache is populated), check that build times are reduced compared to cold builds

Notes

• This change uses the built-in caching mechanism of actions-rust-lang/setup-rust-toolchain@v1 rather than manual cache actions
• Cache misses or failures will not break the build - they'll just result in slower builds like before
• The cache key is automatically generated based on Cargo.lock content, ensuring cache invalidation when dependencies change

Link to Devin run: https://app.devin.ai/sessions/9d14059dbcb54ba1b93b7f9481e3e878
Requested by: Jayant (jayant@dourolabs.xyz)

[devin-ai-integration]

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