feat(#329): Print Java Streams as PHI Expressions

[volodya-lombrozo]

In this PR I added the special integration test that checks how opeo-maven-plugin converts Java Streams to PHI expressions.
It is only the first attempt to convert them, so the representation might (and will) dramatically changed in the future.

Related to #329.

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PR-Codex overview

This PR updates class names and refactors code for clarity.

Detailed summary

• Renamed MulTest to MultiplicationTest
• Updated Mul class to Multiplication
• Added Typed interface to Empty and ArrayConstructor
• Refactored ReturnHandler to handle different return types

The following files were skipped due to too many changes: src/it/streams/src/main/java/org/eolang/streams/Main.java, src/main/java/org/eolang/opeo/decompilation/handlers/CheckCastHandler.java, src/main/java/org/eolang/opeo/decompilation/handlers/InvokedynamicHandler.java, src/it/streams/verify.groovy, src/main/java/org/eolang/opeo/compilation/XmirParser.java, src/main/java/org/eolang/opeo/ast/LocalVariable.java, src/test/java/org/eolang/opeo/ast/CheckCastTest.java, src/main/java/org/eolang/opeo/ast/CheckCast.java, src/main/java/org/eolang/opeo/ast/Return.java, src/test/java/org/eolang/opeo/ast/ReturnTest.java, src/test/java/org/eolang/opeo/ast/DynamicInvocationTest.java, src/it/streams/pom.xml, src/main/java/org/eolang/opeo/ast/DynamicInvocation.java, src/main/java/org/eolang/opeo/ast/Handle.java, src/test/resources/xmir/disassembled/Lambda.xmir, src/test/resources/xmir/disassembled/Main.xmir

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[volodya-lombrozo]

@rultor merge

[rultor]

@rultor merge

@volodya-lombrozo OK, I'll try to merge now. You can check the progress of the merge here

[rultor]

@rultor merge

@volodya-lombrozo Done! FYI, the full log is here (took me 9min)

[0crat]

@volodya-lombrozo Thanks for the contribution! You've earned +60 points for this (+20 as a basis, +40 for 1844 hits-of-code). Please, keep them coming. Your running balance is +100.