Restaking: Change max_slashable_per_epoch from tuple-like structure to named field syntax

[aoikurokawa]

Currently, when we build the InitializeNcnVaultSlasherTicket instruction, we use the args method to add max_slashable_per_epoch data:

        let mut ix_builder = InitializeNcnVaultSlasherTicketBuilder::new();
        ix_builder
            .config(Config::find_program_address(&self.restaking_program_id).0)
            .ncn(ncn)
            .vault(vault)
            .slasher(slasher)
            .ncn_vault_ticket(ncn_vault_ticket)
            .ncn_vault_slasher_ticket(ncn_vault_slasher_ticket)
            .admin(keypair.pubkey())
            .payer(keypair.pubkey())
            .args(100);

While this works, the use of the generic name args lacks clarity.
We can improve clarity by using a method with a more descriptive name:

        let mut ix_builder = InitializeNcnVaultSlasherTicketBuilder::new();
        ix_builder
            ...
            .max_slashable_per_epoch(100);

[coachchucksol]

lgtm!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.40%. Comparing base (00eb1c8) to head (f2dac9e).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #173   +/-   ##
=======================================
  Coverage   79.39%   79.40%           
=======================================
  Files          89       89           
  Lines        9338     9340    +2     
=======================================
+ Hits         7414     7416    +2     
  Misses       1924     1924           

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