add java_get_home

[e-kotov]

New function java_get_home() to get currently set JAVA_HOME. This is just a shortcut to Sys.getenv("JAVA_HOME"), as it is faster to type and can be even faster then used with autocomplete.

Closes #57 .

[Copilot]

Pull Request Overview

This PR adds a new convenience function java_get_home() to retrieve the current JAVA_HOME environment variable value. The function provides a shortcut to Sys.getenv("JAVA_HOME") for improved developer experience.

• New java_get_home() function that returns the JAVA_HOME environment variable
• Function returns empty string when JAVA_HOME is not set
• Comprehensive test coverage and documentation added

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
R/java_env.R	Implements the new java_get_home() function with proper error handling
tests/testthat/test-java_env.R	Adds test cases for both set and unset JAVA_HOME scenarios
man/java_get_home.Rd	Generated documentation for the new function
NAMESPACE	Exports the new function for public use
NEWS.md	Documents the new feature in the changelog

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