test: add http2 handler e2e suite and tighten host-mapper + idle-timeout tests

Add tests/e2e/http2_test.go covering the http2 handler/listener/connector/dialer
end-to-end through the canonical gost-as-client pattern (8 subtests: forward,
auth, bypass, probeResist/metadata, h2 stream multiplexing). Include
testdata/http2/{server,server_auth,server_bypass,server_proberesist,client,
client_auth}.yaml. Note that h2/h2c listeners pair with the tunnel handler
and only http2 listener pairs with handler http2 (reads r/w from metadata).

Tighten TestDNSHostMapper by pointing the handler at an unreachable upstream
so unmapped names fail at the exchanger, confirming the host-mapper path was
the sole reason mapped names resolved. Fix http_idle_timeout.py to speak HTTP
through the CONNECT tunnel rather than a raw ping, matching the echo backend.

Co-Authored-By: Claude <noreply@anthropic.com>

tests/e2e/scripts/http_idle_timeout.py

@@ -28,11 +28,19 @@ def main():
         print(f"FAIL: expected 200, got {resp.decode(errors='replace')}")
         sys.exit(1)
 
-    # Send request through the CONNECT tunnel
-    s.sendall(b"ping-1\n")
-    data = s.recv(4096)
-    if b"ping-1" not in data:
-        print(f"FAIL: expected ping-1 echo, got {data!r}")
+    # Send an HTTP GET through the CONNECT tunnel. The tunnel target
+    # is an HTTP echo server (BaseHTTPRequestHandler), so we must speak
+    # HTTP or the connection closes.
+    req = b"GET / HTTP/1.0\r\nHost: tcp-echo\r\n\r\n"
+    s.sendall(req)
+    data = b""
+    while b"hello-gost" not in data:
+        chunk = s.recv(4096)
+        if not chunk:
+            break
+        data += chunk
+    if b"hello-gost" not in data:
+        print(f"FAIL: expected hello-gost echo, got {data!r}")
         sys.exit(1)
     print(f"PASS: first request through tunnel succeeded")