feat: charge escrow if present

[GabrielePicco]

Ephemeral Escrow Fee Payer Support

• Added the ephemeral_balance_pda_from_payer function in the new escrow module to derive an ephemeral escrow account for a given payer, and integrated it into transaction fee validation so that if the main fee payer account does not exist, the system will attempt to charge fees from the escrow account instead (src/escrow.rs, src/transaction_processor.rs). [1] [2] [3]

CI and Dependency Updates

• Added a GitHub Actions workflow for running Rust tests, and updated Cargo.toml with new dependencies required for escrow and reserved account key support (.github/workflows/cargo-test.yml, Cargo.toml). [1] [2] [3] [4]

[bmuddha]

have a few concerns, and a potentially an escrow account dissociation bug.

[GabrielePicco]

have a few concerns, and a potentially an escrow account dissociation bug.

Verified correct behaviour with integration test: https://github.com/magicblock-labs/magicblock-validator/pull/528/files#diff-eee5d643b14736cae0b44b1bbf83a985a87987b65fcbd1f02a57cd4d3617a52eR15 (which can be merged once the new cloning pipeline is integrated)

[bmuddha]

LGTM overall, with a few minor nits, I need to test the interaction with the accountsdb, that correct feepayer is charged and persisted. And it should be good to merge.

[GabrielePicco]

LGTM overall, with a few minor nits, I need to test the interaction with the accountsdb, that correct feepayer is charged and persisted. And it should be good to merge.

Thanks @bmuddha, applied suggested nits

[bmuddha]

LGTM, higher level integration tests are green