fix: use the config arg in the get_balance rpc method

[0xzrf]

Summary

This PR refactors SurfpoolMinimalRpc::get_balance() to use the config: Option<RpcContextConfig> argument, which provides the commitment: Option<CommitmentConfig> and min_context_slot: Option<u64> variables, in order to customize the get_balance rpc method further

What Changed

• Extracted commitment and min_context_slot variables, and provided Commitment::confirmed()(the default earilier) to commitment and None to min_context_slot in case None
• use the commitment provided in config inside the meta.get_rpc_context() in case present, or Commitment::confirmed() otherwise
• Use the min_context_slot value (if present) to validate the svm_locker.get_account().slot
• Added a SurfpoolError::get_balance() method that returns a SurfpoolError::internal_error() with error.data = "Context slot too old"

Context

This change was motivated by an existing comment inside SurfpoolMinimalRpc::get_balance() that suggested using the config in the function. This PR increases the configurability of the rpc's get_balance method by allowing to provide the commitment level and min_context_slot as arguments

Note

I may or may not have used the min_context_slot value properly, as I've assumed that it's used to validate the value svm_locker.get_account().slot and require it to be bigger then then the argument. I'd be happy to change it's use case in case my assumption is wrong. Thanks

[MicaiahReid]

Thanks for the issue! Some small fixes requested.

[0xzrf]

@MicaiahReid I've made the changes
lmk if you have any feedbacks. Thanks

[MicaiahReid]

Sorry, should have requested earlier, can we also add some tests for these changes?

[MicaiahReid]

Can we remove this error that is no longer being used?

[0xzrf]

Got it

[0xzrf]

@MicaiahReid added some tests that check whether the get_balance rpc method fail when the min_context_slot is bigger then latest_absolute_slot()

lmk if anything else is required. Thanks

[0xzrf]

@MicaiahReid Added config support for the SurfpoolFullRpc::get_fee_for_message in the last commit, ik the PR specifically fixes the get_balance, but theoratically the fixes for both the rpc methods felt the same.

[MicaiahReid]

Almost there!