(test): exclude runtime-only code from coverage

Server/ (Swoole event loops) and Sockmap/ (FFI + BPF kernel code) can
only execute inside a live Swoole process. Exclude them so coverage
reflects the testable library surface: adapters, resolvers, DNS,
protocol detection, validation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: abnegate

phpunit.xml

@@ -13,5 +13,9 @@
         <include>
             <directory>src</directory>
         </include>
+        <exclude>
+            <directory>src/Server</directory>
+            <directory>src/Sockmap</directory>
+        </exclude>
     </source>
 </phpunit>