[feat] engines: add tusksearch (web, news, videos, images) (#6267)

The code that reads the value of variable `x` from `embed.js`, decodes
it to ASCII and based on that sets `window["tuskheader"]` and `window["tuskkey"]`
is attached below. The only real way to figure out what this is doing is
by stepping through it with the debugger, otherwise it's almost hopeless.

```js
function fe() {
  const B = pe => pe.map(_e => String.fromCharCode(_e)).join(''),
  ae = window,
  o = ae.x;
  if (o?.length) {
    const pe = o.length / 2;
    for (let _e = 0; _e < pe; _e++) ae[B(o[_e])] = B(o[pe + _e]);
    ae.x = void 0
  }
}
```

Minimal script for testing the engine:

```py
import random
from json import loads
import requests

resp = requests.get("https://api.tusksearch.com/revcontent/embed.js")
data = loads(resp.text[6:])

def _decode(text: list[int]) -> str:
    return "".join([chr(x) for x in text])

header = _decode(data[3])
value = _decode(data[4])

resp = requests.get(
    "https://api.tusksearch.com/Search/Web?q=test&p=1&l=center&nextArgs=&prevArgs=",
    # "https://api.tusksearch.com/Search/Image?q=test&p=1&l=center",
    headers={
        header: value,
        'x-lon': str(random.random() * 90),
        'x-lat': str(random.random() * 90),
    },
)
print(resp.text)
```

searx/settings.yml

@@ -2383,6 +2383,35 @@ engines:
       - 5000
     inactive: true
 
+  - name: tusksearch
+    engine: tusksearch
+    shortcut: tu
+    tusk_categ: web
+    categories: general
+    disabled: true
+
+  - name: tusksearch images
+    engine: tusksearch
+    shortcut: tui
+    paging: false
+    tusk_categ: images
+    categories: images
+    disabled: true
+
+  - name: tusksearch videos
+    engine: tusksearch
+    shortcut: tuv
+    tusk_categ: videos
+    categories: videos
+    disabled: true
+
+  - name: tusksearch news
+    engine: tusksearch
+    shortcut: tun
+    tusk_categ: news
+    categories: news
+    disabled: true
+
   # tmp suspended - too slow, too many errors
   #  - name: urbandictionary
   #    engine      : xpath