Add jextract module: SQLite bindings generated with jextract, FFM arenas, C strings, out-parameters, errors, upcalls, and a JMH comparison with JNI

jextract-25 early-access build (25-jextract+2-4) on JDK 25.0.5+8 against SQLite 3.45.1: 25 functions and 13 constants
generated into 4 committed files (the whole header would be 83 files), a small Db wrapper, the four arena kinds
used wrongly on purpose, ADDRESS vs C_POINTER zero-length vs unbounded segments and the SIGSEGV from getString
on a NULL pointer, sqlite3_open out-parameter, return codes to exceptions, a sqlite3_exec upcall and the VM exit
when it throws, the JDK 25 native-access warning and --illegal-native-access=deny, library loading failures,
and a JMH benchmark of FFM vs hand-written JNI vs plain Java (indicative only: shared 2-CPU machine).

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b6Kg9RWSTJzyz6KP9X

jextract/output/07-pointer-traps.txt

@@ -0,0 +1,18 @@
+$ java --enable-native-access=ALL-UNNAMED -cp build/classes demo.Trap
+ValueLayout.ADDRESS : byteSize=0
+getString(0)        : IndexOutOfBoundsException, "No null terminator found..."
+reinterpret(100)    : hello from C land
+C_POINTER           : byteSize=9223372036854775807
+getString(0)        : hello from C land
+
+$ java --enable-native-access=ALL-UNNAMED -XX:ErrorFile=/tmp/jextract-hs_err.log -cp build/classes demo.NullText     # first lines of the crash banner
+address=0 byteSize=9223372036854775807 equals(NULL)=true
+about to call getString(0) on it
+#
+# A fatal error has been detected by the Java Runtime Environment:
+#
+#  SIGSEGV (0xb) at pc=0x00007f002fe4645d, pid=20843, tid=20844
+#
+# JRE version: OpenJDK Runtime Environment Temurin-25.0.5+8 (25.0.5+8) (build 25.0.5+8-LTS)
+# Java VM: OpenJDK 64-Bit Server VM Temurin-25.0.5+8 (25.0.5+8-LTS, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, g1 gc, linux-amd64)
+exit code: 134