Since SQLite is embedded in your program, why not use your programming language directly. SQLite can even callback in custom functions you define. For example in Python: https://docs.python.org/3/library/sqlite3.html#sqlite3.Conne....

The main reason why main client-server databases have so many built-in functions is because of the round-trips. Let's say you want to filter rows based on the result of some function, if your function is implemented client-side, then the database would have to send each row to the client.

"Relational database engines act as bandwidth-reducing data filters." (https://www.sqlite.org/whentouse.html)