Minor refactoring

Created by: matthew-d-jones

Description of work

Small refactoring changes for things I came across when looking into another ticket:

• Remove superfluous includes
• Move includes to implementation file from header
• Change produce method to take a string instead of having reinterpret and c-style casts in many places
• Improve erroneous or waffling comments
• Don't use ASSERT_DOUBLE_EQ for integer types

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