refactor: Clean up Client result source logic and allow multiple mutation results

[kitten]

Summary

This cleans up the Client’s createExecutionRequest and makeResultSource logic. Specifically, it groups a couple of code branches, and refactors the reused source to use a simple lazy source rather than a make source.

Furthermore, it will allow multiple mutation results to be issued. A follow-up PR for bindings is needed here.

Set of changes

• Clean up Client logic
• Replace make result source with lazy
• Add takeWhile(result => !!result.hasNext, true) instead of take(1) on mutations