Remove commons-io by replacing its limited usage in Checker

[mraselimo]

While performing static analysis on this project, we noticed that the dependency commons-io is used
only very sparsely, in this case only in a small number of locations within Checker.
This pull request replaces that usage with equivalent functionality from the Java standard library,
allowing commons-io to be removed from pom.xml.

Benefits of this change include:

• Reduced dependency footprint
• Lower maintenance and update overhead
• Slightly simplified build configuration
• Reduced transitive dependency surface

The replacement is functionally equivalent and does not alter the behavior of the affected code.

Additionally, this pull request adds javax.annotation-api explicitly so the existing @PostConstruct
usage continues to compile on modern JDKs where those annotations are no longer bundled.

Please let us know if there are any concerns regarding compatibility or future plans that would justify
retaining commons-io.

Change Summary

• Replaced IOUtils.readLines(...) with standard Java BufferedReader handling
• Replaced IOUtils.closeQuietly(...) with try-with-resources
• Removed commons-io from pom.xml
• Added javax.annotation-api to preserve compilation on modern JDKs

Verification

• Ran mvn -Dmaven.repo.local=/tmp/m2-language-tools-bg test
• Result: BUILD SUCCESS
• Tests run: 2, Failures: 0, Errors: 0, Skipped: 0