refactor: remove builder class and use concrete class

tests: added more unit tests for event processor

config/debug.yml

@@ -0,0 +1,10 @@
+ monolog:
+     handlers:
+       buffered:
+         type:     buffer
+         handler:  easylog
+         channels: ["!event"]
+         level:    debug
+         easylog:
+           type: service
+           id:   easycorp.easylog.handler

config/main.yml

@@ -0,0 +1,6 @@
+services:
+  easycorp.easylog.handler:
+    class: EasyCorp\EasyLog\EasyLogHandler
+    public: false
+    arguments:
+      - '%kernel.logs_dir%/%kernel.environment%.log'