feat: add TCP connect checker plugin

src/proxy_pool/plugins/builtin/checkers/tcp_connect.py

@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+import asyncio
+
+from proxy_pool.config import Settings
+from proxy_pool.plugins.protocols import CheckContext, CheckResult
+
+
+class TcpConnectChecker:
+    name = "tcp_connect"
+    stage = 1
+    priority = 0
+    timeout = 5.0
+
+    def __init__(self, timeout: float = 5.0) -> None:
+        self.timeout = timeout
+
+    async def check(
+        self,
+        proxy_ip: str,
+        proxy_port: int,
+        proxy_protocol: str,
+        context: CheckContext,
+    ) -> CheckResult:
+        try:
+            reader, writer = await asyncio.wait_for(
+                asyncio.open_connection(proxy_ip, proxy_port),
+                timeout=self.timeout,
+            )
+            latency = context.elapsed_ms()
+            context.tcp_latency_ms = latency
+            writer.close()
+            await writer.wait_closed()
+
+            return CheckResult(
+                passed=True,
+                detail="TCP connect OK",
+                latency_ms=latency,
+            )
+        except TimeoutError:
+            return CheckResult(
+                passed=False,
+                detail=f"TCP connect timed out after {self.timeout}s",
+            )
+        except OSError as err:
+            return CheckResult(
+                passed=False,
+                detail=f"TCP connect failed: {err}",
+            )
+
+    def should_skip(self, proxy_protocol: str) -> bool:
+        return False
+
+
+def create_plugin(settings: Settings) -> TcpConnectChecker:
+    return TcpConnectChecker(
+        timeout=settings.proxy.check_tcp_timeout,
+    )