feat(#2642): unphi mojo

[maxonfjvipon]

Ref: #2642

What's done:

• Introduced UnphiMojo
• Added tests for UnphiMojo
• Added grammar for phi-calculus expressions
• Added xembly listener for phi-calculus expression parsing
• Refactored code related to Syntax class

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PR-Codex overview

This PR focuses on renaming classes and files related to the Eo parser.

Detailed summary

• Renamed Program.g4 to Eo.g4.
• Renamed XeListener.java to XeEoListener.java.
• Renamed Syntax class to EoSyntax.
• Updated references to the renamed classes and files.

The following files were skipped due to too many changes: eo-parser/src/test/java/org/eolang/parser/EoLexerTest.java, eo-parser/src/main/java/org/eolang/parser/EoLexer.java, eo-parser/src/main/java/org/eolang/parser/SourceText.java, eo-parser/src/main/java/org/eolang/parser/PhiSyntax.java, eo-maven-plugin/src/main/java/org/eolang/maven/UnphiMojo.java, eo-maven-plugin/src/test/java/org/eolang/maven/UnphiMojoTest.java, eo-parser/src/main/java/org/eolang/parser/Syntax.java, eo-parser/src/main/java/org/eolang/parser/EoSyntax.java, eo-parser/src/test/java/org/eolang/parser/SyntaxTest.java, eo-parser/src/main/java/org/eolang/parser/XePhiListener.java, eo-parser/src/main/java/org/eolang/parser/XeListener.java

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[maxonfjvipon]

@yegor256 please have a look

[yegor256]

@rultor merge

[rultor]

@rultor merge

@yegor256 OK, I'll try to merge now. You can check the progress of the merge here

[rultor]

@rultor merge

@yegor256 Done! FYI, the full log is here (took me 18min)