Feat: simpler gasless implementation (#406)

See #360 

<!-- greptile_comment -->

## Greptile Summary

Major architectural changes to implement native gasless transaction
support by removing automatic airdrops and modifying fee handling across
the validator.

- Modified `magicblock-bank/src/consts.rs` to set
`DEFAULT_LAMPORTS_PER_SIGNATURE` to 0 and integrate with patched
solana-svm for zero-fee transactions
- Removed payer initialization and automatic airdrop functionality from
configs and `magicblock-accounts/src/config.rs`
- Updated genesis configuration in
`magicblock-bank/src/genesis_utils.rs` to support configurable
transaction fees
- Modified `Cargo.toml` to use custom magicblock-labs/magicblock-svm
fork at commit e93eb57
- Added support for executing transactions with non-existent fee payers
in `magicblock-bank/tests/transaction_execute.rs`



<!-- /greptile_comment -->

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

Author: GabrielePicco

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