feat: Cleaner gasless implementation (#360)

## Summary

This PR simplifies the gasless setup by removing the automatic airdrop
and introducing a native way to execute transactions without charging
the payer.

- https://github.com/magicblock-labs/magicblock-svm
- Changed the `solana-svm` dependency to use a patched version that
allows signers without lamports
- Added a test case in `transaction_execute.rs` to verify transactions
with non-existent fee payers and zero fees
- Simplified and modified genesis to set lamports per signature from the
config (base fees)
- Set the default lamports per signature to 0

## Notes

- A follow-up PR will completely remove the initial payer SOL/lamports
configuration and logic
- A follow-up PR will address rent

---------

Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com>

Author: GabrielePicco

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