Solana code quality and reliability improvement

[lumtis]

This EPIC lists different task we should complete to improve the codebase before considering new features integrations like withdrawAndCall

Tasks

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1. make withdraw_spl_token tx successful when "non-existent destination" happened protocol-contracts-solana#63
   +0
2. Implement a customizable deposit fee/threshold protocol-contracts-solana#62
   +0
   
3. Rename programs/protocol-contracts-solana into programs/gateway protocol-contracts-solana#50
   code-quality +1
4. Establish specs for access control for gateway protocol-contracts-solana#47
   +0
5. Add comments for each public methods and improve Gateway program organization protocol-contracts-solana#46
   code-quality +1
6. Complete unit test for the program protocol-contracts-solana#12
   test +1
7. https://github.com/zeta-chain/protocol-private/issues/189
8. https://github.com/zeta-chain/protocol-private/issues/188
9. https://github.com/zeta-chain/protocol-private/issues/187
10. https://github.com/zeta-chain/protocol-private/issues/186
11. https://github.com/zeta-chain/protocol-private/issues/185
12. https://github.com/zeta-chain/protocol-private/issues/184
13. https://github.com/zeta-chain/protocol-private/issues/183
14. https://github.com/zeta-chain/protocol-private/issues/182
15. https://github.com/zeta-chain/protocol-private/issues/181
16. https://github.com/zeta-chain/protocol-private/issues/180
17. https://github.com/zeta-chain/infrastructure/issues/1848
18. e2e: add stress tests for Solana deposit and withdraw #2785
    E2E chain:solana +2