Shuttle Christmas Code Hunt 2023 - Axum Edition

I've re-started the Christmas Code Hunt using the Axum Web framework.

2023-12-19

• quickly re-built the minus1 challenge endpoints
• validated them successfully against cch23-validator
• completed Day 12, Task 1 and validated it: success

2023-12-20

• started Day 13, Task 1
• stubbed out the /13/sql endpoint
• added database pool to application state
• added shuttle_shared_db and sqlx to dependencies
• completed Task 1, validated successfully with cch23-validator