Fix OpenCL reserved keyword local variable generation

[Thanhdn1984]

Summary

• Escape Java local variable names that collide with OpenCL reserved words during kernel code generation.
• Apply the same escaping to generated kernel argument names.
• Add a regression codegen test covering local variables named kernel and global.

Fixes #54

Verification

• git diff --check
• Could not run Maven tests locally: this container has no mvn, javac, or jshell installed.