NIAD-2797: ReferralRequest priority should not use 'Stat'

[MartinWheelerMT]

What

Updated the Referral Request Mapper to use 'ASAP' instead of 'Stat' when mapping and add unit tests to cover these scenarios.
Have also refactored the tests for Referral Request Mapper and the mapper itself.

Why

As per the documentation: Request Priority we should be using 'stat' not 'asap' when mapping referral request priority codes.

Type of change

Please delete options that are not relevant.

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I have performed a self-review of my code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have updated the Changelog with details of my change in the UNRELEASED section if this change will affect end users
• A corresponding change has been made to the Mapping Documentation repository

[adrianclay]

I wonder if this is a breaking change 🤣 🤔.

[MartinWheelerMT]

I can update to report as breaking change!

[adrianclay]

Enjoyed the assertAll, tried playing with it locally and felt somewhat disappointed at verbose output JUnit produces. One day Java will learn what concise means.