Remove strval from src/Data/Provisioners/DBRowProvisioner.php

[driusan]

The DBRowProvisioner casts all values (that aren't null) from the database to string using strval, in order to maintain compatibility between versions of PHP where the PDO returns a string and versions of PHP where the PDO returns a typed value based on the database schema type.

We no longer need to support any version of PHP where the former is the case on the main branch, so we can remove the string conversion and rely on the database typing.