feat: support Java 17 release target

[Axionize]

Summary

• Add Java 17 runtime support by targeting Java 17 bytecode by default.
• Replace Java 21-only APIs with Java 17-compatible equivalents in runtime, tests, and JMH sources.
• Update public docs and compatibility notes from Java 21 baseline to Java 17+.

Verification

• ./gradlew test
• ./gradlew jmhClasses
• ./gradlew examplesClasses
• Documentation updated where behavior or public API changed
• Also ran the same checks with an explicit JDK 17 toolchain.

Benchmark Notes

I ran a separate Java release-target matrix on two machines to check whether Java 17-targeted bytecode regressed the fixed-path benchmarks when run on newer JVMs.

• Summary: https://github.com/Axionize/Lattice/tree/master/docs/benchmark-results/java-release-target-matrix
• Ryzen 9 9950X: https://github.com/Axionize/Lattice/blob/master/docs/benchmark-results/java-release-target-matrix/ryzen-9-9950x.md
• Xeon E5-2699A v4: https://github.com/Axionize/Lattice/blob/master/docs/benchmark-results/java-release-target-matrix/xeon-e5-2699av4.md
• Harness: https://github.com/Axionize/Lattice/tree/master/scripts/jmh-matrix

Result: the Ryzen 9 9950X run did not show a material slowdown from Java 17-targeted bytecode on OptimalPathBenchmark.latticeInlineFusedCompleted; all release-target comparisons for that benchmark were within overlapping JMH error
intervals.

Notes

• The release target can be overridden with -Plattice.javaRelease=<version>.
• The build toolchain can be overridden with -Plattice.javaToolchain=<version>.