refactor: split test.py into modular pytest integration tests + benchmark tool

- tests/integration/common.py: ServerManager (reuses server across tests),
  run_client, test data generation, verification utilities
- tests/integration/test_tcp.py: 14 TCP transport correctness tests
- tests/integration/test_ssh.py: 10 SSH transport tests (skip when unavailable)
- tests/integration/test_tls.py: 5 TLS encryption tests (new coverage!)
- tests/integration/test_features.py: 13 feature tests (incremental, delete,
  exclude, include, max/min size, bwlimit, dry run, archive, progress)
- tests/integration/test_preflight.py: 7 CLI validation/error tests
- benchmark/bench.py: standalone benchmark with JSON output, p50/p95, multi-run
- Updated Dockerfile with python3-pytest, openssl, openssh-client
- Updated CI to use pytest (gitea.tap-tap.win/taptap/fastsync-ci:v6)
- Removed old monolithic test.py

tests/integration/test_tcp.py

@@ -0,0 +1,111 @@
+"""TCP transport correctness tests."""
+import os
+import sys
+import pytest
+
+sys.path.insert(0, os.path.dirname(__file__))
+from common import (
+    PROJECT_ROOT, BUILD_DIR, TEST_DATA_DIR,
+    ServerManager, run_client, run_client_posix,
+    generate_test_files, verify_transfer, clean_dir, make_result,
+    get_dest_received_dir, CLIENT_CMD,
+)
+
+SOURCE_DIR = os.path.join(TEST_DATA_DIR, "tcp_source")
+DEST_DIR = os.path.join(TEST_DATA_DIR, "tcp_dest")
+
+
+@pytest.fixture(scope="module", autouse=True)
+def setup_test_data():
+    generate_test_files(SOURCE_DIR, full=False)
+    clean_dir(DEST_DIR)
+    yield
+    import shutil
+    shutil.rmtree(TEST_DATA_DIR, ignore_errors=True)
+
+
+def _run_tcp_test(name, flags, use_metadata=True, posix=False):
+    """Run a single TCP test case with a fresh server."""
+    clean_dir(DEST_DIR)
+    with ServerManager() as server:
+        if posix:
+            result, dur = run_client_posix(SOURCE_DIR, DEST_DIR,
+                                           flags=(["-M"] if use_metadata else []) + flags,
+                                           port=server.port)
+        else:
+            result, dur = run_client(SOURCE_DIR, DEST_DIR,
+                                     flags=(["-M"] if use_metadata else []) + flags,
+                                     port=server.port)
+
+    if result.returncode != 0:
+        return make_result(name, False, dur, f"Exit {result.returncode}: {(result.stderr or result.stdout)[:100]}")
+
+    received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+    mismatches, missing = verify_transfer(SOURCE_DIR, received)
+    if missing:
+        return make_result(name, False, dur, f"Missing: {', '.join(missing[:5])}")
+    if mismatches:
+        return make_result(name, False, dur, f"Mismatch: {', '.join(mismatches[:3])}")
+    return make_result(name, True, dur)
+
+
+class TestTCPStandard:
+    def test_standard(self):
+        r = _run_tcp_test("Standard", [])
+        assert r["status"] == "Success", r["error"]
+
+    def test_posix_args(self):
+        r = _run_tcp_test("Posix Args", [], posix=True)
+        assert r["status"] == "Success", r["error"]
+
+    def test_no_metadata(self):
+        r = _run_tcp_test("Standard (no metadata)", [], use_metadata=False)
+        assert r["status"] == "Success", r["error"]
+
+
+class TestTCPFlags:
+    def test_multithreading(self):
+        r = _run_tcp_test("Multithreading (-m)", ["-m"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_compression(self):
+        r = _run_tcp_test("Compression (-c)", ["-c"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_chunk_serialization(self):
+        r = _run_tcp_test("Chunk Serialization (-s)", ["-s"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_compression_chunk(self):
+        r = _run_tcp_test("Compression + Chunk (-c -s)", ["-c", "-s"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_multithread_compression(self):
+        r = _run_tcp_test("Multithreading + Compression (-m -c)", ["-m", "-c"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_multithread_chunk(self):
+        r = _run_tcp_test("Multithreading + Chunk (-m -s)", ["-m", "-s"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_all_flags(self):
+        r = _run_tcp_test("Multithread + Compression + Chunk (-m -c -s)", ["-m", "-c", "-s"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_sendfile(self):
+        r = _run_tcp_test("Sendfile (-f)", ["-f"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_sendfile_multithread(self):
+        r = _run_tcp_test("Sendfile + Multithreading (-f -m)", ["-f", "-m"])
+        assert r["status"] == "Success", r["error"]
+
+
+class TestTCPChunkSize:
+    def test_custom_chunk_size(self):
+        r = _run_tcp_test("Chunk size 5MB", ["--chunk-size", "5242880"])
+        assert r["status"] == "Success", r["error"]
+
+    def test_small_chunk_size(self):
+        r = _run_tcp_test("Chunk size 1KB", ["--chunk-size", "1024"])
+        assert r["status"] == "Success", r["error"]