fix(netxlite): http factory that propagates close-idle-connections (#465)

While there reorganize mocks' tls implementation to use a single file
called tls.go (and tls_test.go) just like netxlite does.

While there write tests ensuring we always add timeouts when we are
making TCP connections (be them TLS or cleartext).

See https://github.com/ooni/probe/issues/1591

internal/netxlite/mocks/tls.go

@@ -0,0 +1,60 @@
+package mocks
+
+import (
+	"context"
+	"crypto/tls"
+	"net"
+)
+
+// TLSHandshaker is a mockable TLS handshaker.
+type TLSHandshaker struct {
+	MockHandshake func(ctx context.Context, conn net.Conn, config *tls.Config) (
+		net.Conn, tls.ConnectionState, error)
+}
+
+// Handshake calls MockHandshake.
+func (th *TLSHandshaker) Handshake(ctx context.Context, conn net.Conn, config *tls.Config) (
+	net.Conn, tls.ConnectionState, error) {
+	return th.MockHandshake(ctx, conn, config)
+}
+
+// TLSConn allows to mock netxlite.TLSConn.
+type TLSConn struct {
+	// Conn is the embedded mockable Conn.
+	Conn
+
+	// MockConnectionState allows to mock the ConnectionState method.
+	MockConnectionState func() tls.ConnectionState
+
+	// MockHandshakeContext allows to mock the HandshakeContext method.
+	MockHandshakeContext func(ctx context.Context) error
+}
+
+// ConnectionState calls MockConnectionState.
+func (c *TLSConn) ConnectionState() tls.ConnectionState {
+	return c.MockConnectionState()
+}
+
+// HandshakeContext calls MockHandshakeContext.
+func (c *TLSConn) HandshakeContext(ctx context.Context) error {
+	return c.MockHandshakeContext(ctx)
+}
+
+// TLSDialer allows to mock netxlite.TLSDialer.
+type TLSDialer struct {
+	// MockCloseIdleConnections allows to mock the CloseIdleConnections method.
+	MockCloseIdleConnections func()
+
+	// MockDialTLSContext allows to mock the DialTLSContext method.
+	MockDialTLSContext func(ctx context.Context, network, address string) (net.Conn, error)
+}
+
+// CloseIdleConnections calls MockCloseIdleConnections.
+func (d *TLSDialer) CloseIdleConnections() {
+	d.MockCloseIdleConnections()
+}
+
+// DialTLSContext calls MockDialTLSContext.
+func (d *TLSDialer) DialTLSContext(ctx context.Context, network, address string) (net.Conn, error) {
+	return d.MockDialTLSContext(ctx, network, address)
+}