Refactor `CalculateGas` to use proto-generated service client

[amaury1093]

Summary of Refactor

Use the generated tx service client instead of hardcoding the gRPC route

ref: #7688 (comment)

Version

82f15f3

Description

Currently, the calculate gas makes a Tendermint query with a hardcoded gRPC route to the simulate service. This works, but we should prefer to use the generated client.

Proposed Refactor

• Remove the hardcoded gRPC service method route: https://github.com/cosmos/cosmos-sdk/blob/master/client/tx/tx.go#L289-L300
• Use the new tx service introduced in Add GetTx gRPC endpoint #7688

txServiceClient = tx.NewServiceClient(clientCtx)
txServiceClient.Simulate(...)

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