Feat: Apply Google Java Style Guide formatting and naming conventions

[4Empty4]

This commit addresses multiple Checkstyle and style guide violations across the source files:

Refactor: Renamed package core.basesyntax.Model to core.basesyntax.model to comply with the all-lowercase package naming rule.

Style: Ensured imports are sorted lexicographically (ASCII) and placed in a single, unseparated block.

Style: Standardized operator wrapping by placing the concatenation operator (+) at the beginning of the new line.

Style: Fixed line length violations (max 100 characters) in HelloWorld's sayHello method.

Style: Renamed single-letter field a to memberName to meet lowerCamelCase style requirements for members.

Style: Ensured correct vertical spacing (one newline) between package/imports/class declaration and between class members.

Style: Added a newline at the end of the file for compliance.