Use MySQL rows as associative arrays and name all columns

Currently, the MySQL rows use a mix of enumerated and associative arrays.

Plan is to restrict by default in Keruald Database the fetch_row() method
to use associative array.

Goal is to ease API serialization and ensure proper code handling:

• no SELECT *, every column should be named
• SELECT <formula> uses aliases: SELECT <formula> as <descriptive name>

Reference: https://www.php.net/manual/en/mysqli-result.fetch-array.php