Java bindings: evaluate replacing hand-written JNI with the Foreign Function & Memory API

The Java bindings added in #1524 are hand-written JNI. Java 22 and later ship the Foreign Function & Memory API (JEP 454), which calls the C API directly and would remove cuopt_jni.cpp and its build entirely.

Why it was not done now: the bindings target Java 17, which is still a common default. An earlier revision of #1524 did use FFM and required Java 22 or higher.

Trade-off to settle:

• Hand-written JNI keeps the Java 17 floor, but every static native declaration and its entry point must be kept in sync by hand. #1524 adds scripts/check_jni_symbols.sh to catch drift, since JNI resolves lazily and a mismatch otherwise surfaces only when something calls the method.
• FFM removes the native shim and the drift class of bug, at the cost of requiring Java 22+.

cuVS uses FFM (via jextract) for its Java interface, so there is in-house precedent for the tooling.

Raised by @mlubin in review: https://github.com/NVIDIA/cuopt/pull/1524#discussion_r3839538078

Part of #1535.