Add FFI subsystem with languages and Makefile

Introduce a multi-language FFI layer and build/test integration. Adds a C-core ABI (ffi/c_core/pal_ffi.h, pal_ffi.c) exposing allocator, event-loop, FTP and HTTP server primitives, plus language bindings and tests: Java (JNI wrapper, Java classes, tests, bench), Go (cgo wrapper + tests), Python (CFFI module + pytest tests, benchmarks), and Rust (crate, benches/tests). Add feasibility/benchmark report and helper benchmark scripts. Integrate FFI into the Makefile with new ffi targets (ffi, ffi-java, ffi-rust, ffi-python, ffi-go), shared-library build rules, object rules, and minor .gitignore updates; also includes other test files and a modification to src/http_api.c.

ffi/benchmarks/BenchJava.java

@@ -0,0 +1,43 @@
+package org.zftpd.ffi;
+
+public class BenchJava {
+
+    public static void benchmarkAllocator(int iterations) {
+        PalAlloc.initDefault();
+        long start = System.nanoTime();
+        
+        for (int i = 0; i < iterations; i++) {
+            long ptr = PalAlloc.malloc(64);
+            PalAlloc.free(ptr);
+        }
+        
+        long end = System.nanoTime();
+        double ms = (end - start) / 1_000_000.0;
+        System.out.printf("[Java] Allocator (%d iters): %.2f ms\n", iterations, ms);
+    }
+
+    public static void benchmarkFtpStartup(int iterations) {
+        long start = System.nanoTime();
+        
+        for (int i = 0; i < iterations; i++) {
+            int port = 20000 + (i % 10000);
+            try (FtpServer server = new FtpServer("127.0.0.1", port, "/tmp")) {
+                if (server.start() == 0) {
+                    server.stop();
+                }
+            } catch (Exception e) {
+                // Ignore, as ports may be closing
+            }
+        }
+        
+        long end = System.nanoTime();
+        double ms = (end - start) / 1_000_000.0;
+        System.out.printf("[Java] FtpServer start/stop (%d iters): %.2f ms\n", iterations, ms);
+    }
+
+    public static void main(String[] args) {
+        System.out.println("--- Java FFI Benchmarks ---");
+        benchmarkAllocator(100_000);
+        benchmarkFtpStartup(1000);
+    }
+}