Escape OpenCL keyword identifiers

[justwe-bot]

Fixes #54.

Summary

• add an OpenCL reserved identifier guard in BlockWriter
• mangle Java identifiers that collide with OpenCL keywords by prefixing aparapi_
• apply the same mangling to generated field names, kernel arguments, local variables, array length/dimension helper names, getter output, and object struct fields
• add a codegen regression test using legal Java identifiers that are OpenCL keywords: constant, kernel, and global

Verification

git diff --check

I could not run the Java test suite locally because this environment does not have a Java runtime or Maven installed:

java: Unable to locate a Java Runtime
mvn: command not found

The focused test added is OpenCLKeywordIdentifierTest, which asserts the generated OpenCL uses aparapi_constant, aparapi_kernel, and aparapi_global instead of raw OpenCL keyword identifiers.

Payout preference if needed: USDT/USDT0 on Arbitrum One, 0x69c25c0b82093513abaf8d9c50d17e0564e91505.