Resolve test paths from code source

- Add the ProjectPaths test helper that derives the module root from the test class code source and the repository root from the settings file above it
- Replace the working-directory-relative source and resource literals in thirty-five test classes with module and repository lookups
- Drop the bespoke source-root walk in PregenMantleCleanupContractTest

adapters/bukkit/plugin/src/test/java/art/arcane/iris/testsupport/ProjectPaths.java

@@ -0,0 +1,81 @@
+package art.arcane.iris.testsupport;
+
+import java.io.File;
+import java.net.URISyntaxException;
+import java.net.URL;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.security.CodeSource;
+import java.security.ProtectionDomain;
+
+public final class ProjectPaths {
+    private static final Path MODULE_ROOT = resolveModuleRoot();
+    private static final Path REPOSITORY_ROOT = resolveRepositoryRoot(MODULE_ROOT);
+
+    private ProjectPaths() {
+    }
+
+    public static Path moduleRoot() {
+        return MODULE_ROOT;
+    }
+
+    public static Path repositoryRoot() {
+        return REPOSITORY_ROOT;
+    }
+
+    public static Path moduleFile(String relative) {
+        return MODULE_ROOT.resolve(relative).normalize();
+    }
+
+    public static Path repositoryFile(String relative) {
+        return REPOSITORY_ROOT.resolve(relative).normalize();
+    }
+
+    public static File moduleFileAt(String relative) {
+        return moduleFile(relative).toFile();
+    }
+
+    public static File repositoryFileAt(String relative) {
+        return repositoryFile(relative).toFile();
+    }
+
+    private static Path resolveModuleRoot() {
+        ProtectionDomain domain = ProjectPaths.class.getProtectionDomain();
+        CodeSource source = domain == null ? null : domain.getCodeSource();
+        URL location = source == null ? null : source.getLocation();
+
+        if (location != null) {
+            try {
+                Path current = Path.of(location.toURI()).toAbsolutePath().normalize();
+
+                while (current != null) {
+                    Path name = current.getFileName();
+
+                    if (name != null && "build".equals(name.toString()) && current.getParent() != null) {
+                        return current.getParent();
+                    }
+
+                    current = current.getParent();
+                }
+            } catch (URISyntaxException | IllegalArgumentException ignored) {
+                return Path.of("").toAbsolutePath().normalize();
+            }
+        }
+
+        return Path.of("").toAbsolutePath().normalize();
+    }
+
+    private static Path resolveRepositoryRoot(Path moduleRoot) {
+        Path current = moduleRoot;
+
+        while (current != null) {
+            if (Files.isRegularFile(current.resolve("settings.gradle"))) {
+                return current;
+            }
+
+            current = current.getParent();
+        }
+
+        return moduleRoot;
+    }
+}