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
• After - 2.85s

[scyzoryck]

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

[beberlei]

@scyzoryck thank you very much! 🙇