fix: use Rustls NoCertificateVerification for underscore domains instead of AcceptInvalidCertificates

Remove AcceptInvalidCertificates overrides in configure.rs and qr.rs that
caused a fallback to OpenSSL/native-tls. The upstream Rustls TLS layer now
handles underscore-prefixed domains via NoCertificateVerification directly.
Also fix clippy lint in peer_channels.rs (map_or -> is_some_and).

src/configure.rs

@@ -581,13 +581,7 @@ async fn get_configured_param(
         smtp_password,
         provider,
         certificate_checks: match param.certificate_checks {
-            EnteredCertificateChecks::Automatic => {
-                if param_domain.starts_with('_') {
-                    ConfiguredCertificateChecks::AcceptInvalidCertificates
-                } else {
-                    ConfiguredCertificateChecks::Automatic
-                }
-            }
+            EnteredCertificateChecks::Automatic => ConfiguredCertificateChecks::Automatic,
             EnteredCertificateChecks::Strict => ConfiguredCertificateChecks::Strict,
             EnteredCertificateChecks::AcceptInvalidCertificates
             | EnteredCertificateChecks::AcceptInvalidCertificates2 => {