Gradle build task improvements (#2164)

## Description

This fixes a few problems with the Gradle `build` task and subtasks.
1. Spotless was being run on `node_modules`, resulting in errors for
out-of-source files. This is now disabled.
2. All tests were running from the `build` task, resulting in unexpected
windows popping up. Now only headless tests are run.
3. Headless tests were updated to run from the same root directory as
the other tests.

## Meta

Merge checklist:
- [X] Pull Request title is [short, imperative
summary](https://cbea.ms/git-commit/) of proposed changes
- [X] The description documents the _what_ and _why_
- [ ] If this PR changes behavior or adds a feature, user documentation
is updated
- [ ] If this PR touches photon-serde, all messages have been
regenerated and hashes have not changed unexpectedly
- [ ] If this PR touches configuration, this is backwards compatible
with settings back to v2025.3.2
- [ ] If this PR touches pipeline settings or anything related to data
exchange, the frontend typing is updated
- [ ] If this PR addresses a bug, a regression test for it is added

photon-core/src/test/java/org/photonvision/common/configuration/NetworkConfigTest.java

@@ -25,6 +25,7 @@ import java.io.File;
 import java.io.IOException;
 import java.nio.file.Path;
 import org.junit.jupiter.api.Test;
+import org.photonvision.common.util.TestUtils;
 
 public class NetworkConfigTest {
     @Test
@@ -39,13 +40,13 @@ public class NetworkConfigTest {
     @Test
     public void testDeserializeTeamNumberOrNtServerAddress() {
         {
-            var folder = Path.of("test-resources/network-old-team-number");
+            var folder = TestUtils.getResourcesFolderPath(true).resolve("network-old-team-number");
             var configMgr = new ConfigManager(folder, new LegacyConfigProvider(folder));
             configMgr.load();
             assertEquals("9999", configMgr.getConfig().getNetworkConfig().ntServerAddress);
         }
         {
-            var folder = Path.of("test-resources/network-new-team-number");
+            var folder = TestUtils.getResourcesFolderPath(true).resolve("network-new-team-number");
             var configMgr = new ConfigManager(folder, new LegacyConfigProvider(folder));
             configMgr.load();
             assertEquals("9999", configMgr.getConfig().getNetworkConfig().ntServerAddress);