[ZEPPELIN-6268] Fix resource leaks and add null checks for getResourceAsStream

[renechoi]

What is this PR for?

This PR fixes resource management issues throughout the Zeppelin codebase, specifically addressing resource leaks and potential NullPointerExceptions.

What type of PR is it?

Bug Fix / Improvement

What is the Jira issue?

(Please create a JIRA issue if needed)

How should this be tested?

• All modified files compile successfully
• Existing tests should pass without modification
• The changes maintain backward compatibility

Screenshots (if appropriate)

N/A

Questions:

• Does the license files need update? No
• Is there breaking changes for older versions? No
• Does this need documentation? No (internal improvements only)

Changes Made:

1. AlluxioInterpreterTest.java

• Fixed FileInputStream resource leak by using try-finally block
• Ensures stream is closed even when exceptions occur

2. Resource Loading Null Checks

Added null checks for getResourceAsStream() calls in:

• ZeppelinR.java: Loading R/zeppelin_sparkr.R
• PythonInterpreter.java: Loading Python resources (also fixed missing InputStream import)
• IPythonInterpreter.java: Loading python/zeppelin_ipython.py, python/zeppelin_context.py, and additional init files
• IRInterpreter.java: Loading R/zeppelin_isparkr.R

Benefits:

• Prevents resource leaks that could cause memory issues in long-running processes
• Prevents NullPointerException when resources are missing
• Provides clear error messages when resources cannot be found
• Improves overall stability and reliability

Testing Notes:

While I couldn't run all tests due to environment setup issues, all files compile successfully and the changes are minimal and safe - they only add defensive programming practices without changing any business logic.