Benchmark and UI test integration into gradle

[kristofmoldovan]

Hi!

I integrated the benchmarks into the gradle building system. 😄

The benchmarks can be ran with the "jmh" gradle task.

The following changes were made:

• Created the JMH sourceSet containing all the benchmark classes
• The main game classes were put into a package (I needed to do this because the benchmarks have to import these files, because of this, I imported this package into all the JUnit tests as well)
• Also included the AssertJ Swing dependency for the UI tests in the gradle.build file
• Updated the UI test imports, so they seem to be working now

Please verify if everything is okay 😄

[gergobuzas]

Thank you!

Everything seems fine! However, I'll have to decline this PR, as Attila has already merged your branch into his, and he will send a PR soon to main!