Redefine singleton test scenario and implement new patterns

[mperor]

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[github-actions]

Test Results

220 tests  +1   217 ✅  - 1   4s ⏱️ ±0s
 69 suites  - 1     3 💤 +2 
 69 files    - 1     0 ❌ ±0 

Results for commit af8af1e. ± Comparison against base commit 8719eec.

This pull request removes 2 and adds 3 tests. Note that renamed tests count towards both.

pl.mperor.lab.java.design.pattern.creational.singleton.LazyInitializedSingletonTest ‑ shouldOnlyAllowToLazyCreateOneInstanceOfSingleton()
pl.mperor.lab.java.design.pattern.creational.singleton.SingletonTest ‑ shouldOnlyAllowToCreateOneInstanceOfSingleton()

pl.mperor.lab.java.design.pattern.creational.singleton.SingletonTest ‑ testLazyInitialized()
pl.mperor.lab.java.design.pattern.creational.singleton.SingletonTest ‑ testSerializationSafe()
pl.mperor.lab.java.design.pattern.creational.singleton.SingletonTest ‑ testThreadSafe()