[mod] client/simple: client plugins (#5406)

* [mod] client/simple: client plugins

Defines a new interface for client side *"plugins"* that coexist with server
side plugin system. Each plugin (e.g., `InfiniteScroll`) extends the base
`ts Plugin`. Client side plugins are independent and lazy‑loaded via `router.ts`
when their `load()` conditions are met. On each navigation request, all
applicable plugins are instanced.

Since these are client side plugins, we can only invoke them once DOM is fully
loaded. E.g. `Calculator` will not render a new `answer` block until fully
loaded and executed.

For some plugins, we might want to handle its availability in `settings.yml`
and toggle in UI, like we do for server side plugins. In that case, we extend
`py Plugin` instancing only the information and then checking client side if
[`settings.plugins`](https://github.com/inetol/searxng/blob/1ad832b1dc33f3f388da361ff2459b05dc86a164/client/simple/src/js/toolkit.ts#L134)
array has the plugin id.

* [mod] client/simple: rebuild static

client/simple/src/js/plugin/Calculator.ts

@@ -0,0 +1,93 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import {
+  absDependencies,
+  addDependencies,
+  create,
+  divideDependencies,
+  eDependencies,
+  evaluateDependencies,
+  expDependencies,
+  factorialDependencies,
+  gcdDependencies,
+  lcmDependencies,
+  log1pDependencies,
+  log2Dependencies,
+  log10Dependencies,
+  logDependencies,
+  modDependencies,
+  multiplyDependencies,
+  nthRootDependencies,
+  piDependencies,
+  powDependencies,
+  roundDependencies,
+  signDependencies,
+  sqrtDependencies,
+  subtractDependencies
+} from "mathjs/number";
+import { Plugin } from "../Plugin.ts";
+import { appendAnswerElement } from "../util/appendAnswerElement.ts";
+import { getElement } from "../util/getElement.ts";
+
+/**
+ * Parses and solves mathematical expressions. Can do basic arithmetic and
+ * evaluate some functions.
+ *
+ * @example
+ * "(3 + 5) / 2" = "4"
+ * "e ^ 2 + pi" = "10.530648752520442"
+ * "gcd(48, 18) + lcm(4, 5)" = "26"
+ *
+ * @remarks
+ * Depends on `mathjs` library.
+ */
+export default class Calculator extends Plugin {
+  public constructor() {
+    super("calculator");
+  }
+
+  /**
+   * @remarks
+   * Compare bundle size after adding or removing features.
+   */
+  private static readonly math = create({
+    ...absDependencies,
+    ...addDependencies,
+    ...divideDependencies,
+    ...eDependencies,
+    ...evaluateDependencies,
+    ...expDependencies,
+    ...factorialDependencies,
+    ...gcdDependencies,
+    ...lcmDependencies,
+    ...log10Dependencies,
+    ...log1pDependencies,
+    ...log2Dependencies,
+    ...logDependencies,
+    ...modDependencies,
+    ...multiplyDependencies,
+    ...nthRootDependencies,
+    ...piDependencies,
+    ...powDependencies,
+    ...roundDependencies,
+    ...signDependencies,
+    ...sqrtDependencies,
+    ...subtractDependencies
+  });
+
+  protected async run(): Promise<string | undefined> {
+    const searchInput = getElement<HTMLInputElement>("q");
+    const node = Calculator.math.parse(searchInput.value);
+
+    try {
+      return `${node.toString()} = ${node.evaluate()}`;
+    } catch {
+      // not a compatible math expression
+      return;
+    }
+  }
+
+  protected async post(result: string): Promise<void> {
+    appendAnswerElement(result);
+  }
+}