Refactor system_tables + locking_tx_datastore tests with functions

[Centril]

Description of Changes

Adds some helper functions like column_row that help out in system_tables and in locking_tx_datastore tests.
This helps out with SATS shrinking by dealing with strings in a more central location. (first commit)

Also simplifies some test setup code (second commit).

API and ABI

• This is a breaking change to the module ABI
• This is a breaking change to the module API
• This is a breaking change to the ClientAPI
• This is a breaking change to the SDK API

If the API is breaking, please state below what will break

[cloutiertyler]

Please revert the changes to the systems_table.rs file. See my comment inline for informatino.

[cloutiertyler]

I'm going to veto these changes. This is some of the most critical code in the whole system, and the changes here make it more difficult to read and less obvious as to what is really going on. Particularly with the field names not inline like they were. The additional level of indirection just adds potential for confusion. This code is only going to be written once but read many times.

Additionally this change seems unrelated to Sats, no?

[Centril]

Closing, see Tyler's comment above :)