update setup

• build: remove composer.lock from template
• build: add WP Desk as package author
• build: declare latest low support version
• build: remove composer's platform check
• build: add phpstan as direct dependency/update phpunit
• refactor: update phpunit setup and example test
• build: update phpstan config

phpstan.neon.dist

 # Start command: composer update --classmap-authoritative && vendor/bin/phpstan analyze
-
-includes:
-    - vendor/wpdesk/wp-wpdesk-composer/director/vendor/phpstan/phpstan/conf/bleedingEdge.neon
-    - vendor/wpdesk/wp-wpdesk-composer/director/vendor/szepeviktor/phpstan-wordpress/extension.neon
 parameters:
-    level: max
+    level: 6
     paths:
-        - %currentWorkingDirectory%/src/
+        - src/
     bootstrapFiles:
-        - %currentWorkingDirectory%/vendor/autoload.php
-        - %currentWorkingDirectory%/vendor/wpdesk/wp-wpdesk-composer/director/woocommerce-stubs.php
-    ignoreErrors:
+        - vendor/wpdesk/wp-wpdesk-composer/director/woocommerce-stubs.php