feat(client): add rich domain classes, helpers, and refactor GitLabClient internals

ts/gitlab.classes.protectedbranch.ts

@@ -0,0 +1,21 @@
+import type { IGitLabProtectedBranch } from './gitlab.interfaces.js';
+
+export class GitLabProtectedBranch {
+  public readonly id: number;
+  public readonly name: string;
+  public readonly allowForcePush: boolean;
+
+  constructor(raw: IGitLabProtectedBranch) {
+    this.id = raw.id;
+    this.name = raw.name || '';
+    this.allowForcePush = raw.allow_force_push ?? false;
+  }
+
+  toJSON(): IGitLabProtectedBranch {
+    return {
+      id: this.id,
+      name: this.name,
+      allow_force_push: this.allowForcePush,
+    };
+  }
+}