Improve performance of Assertion Chain class

[scyzoryck]

Hello!

During testing performance of the package with PHPBench I've realised that Reflections methods and checking if method exists takes a lot of time. With the simple fixes we can cut execution time by around 10-15% for lazy assertions.

Benchmark can be found here: scyzoryck/php-validators-benchmark

I'm attaching blackfire profiles:

• [Before - 3.64s](https://blackfire.io/profiles/a89a7ccf-1508-430f-bf76-bc5734564dd4/graph?settings%5Bdimension%5D=wt&settings%5Bdisplay%5D=landscape&settings%5BtabPane%5D=nodes&selected=&callname=main())
• [After - 2.85s](https://blackfire.io/profiles/50d53474-8c48-4e52-b556-80144f4075e0/graph?settings%5Bdimension%5D=wt&settings%5Bdisplay%5D=landscape&settings%5BtabPane%5D=nodes&selected=&callname=main())

[scyzoryck]

@beberlei - is there any change to take a look at this changes, please? :)

[beberlei]

@scyzoryck thank you very much! :bow: