refactor: prefer `psr/log` over static access

Logger previously used in this library is deprecated because of direct file access for a no-longer recommended wpdesk_debug.log. Additionally, previous logger was not listed neither in direct dependencies or suggested packages, what might worsen the discoverability.

This commit introduces standard logger access, using PSR-3 interface, which should be preferred among clients.

Signed-off-by: Bart Jaskulski bjaskulski@protonmail.com