[girlswithmuscle] add support (#4493 #6016)

* [girlswithmuscle] init
* [girlswithmuscle]: fix metadata extraction (site layout change)
* [girlswithmuscle]: fix tags extraction (site layout change)
* update login code
* update 'post' extractor
* update 'gallery' extractor, rename to 'search' extractor
* update docs
* add test cases

---------

Co-authored-by: Mike Fährmann <mike_faehrmann@web.de>

test/results/girlswithmuscle.py

@@ -0,0 +1,55 @@
+# -*- coding: utf-8 -*-
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+
+from gallery_dl.extractor import girlswithmuscle
+
+
+__tests__ = (
+{
+    "#url"     : "https://www.girlswithmuscle.com/2526619/",
+    "#category": ("", "girlswithmuscle", "post"),
+    "#class"   : girlswithmuscle.GirlswithmusclePostExtractor,
+    "#results" : "https://www.girlswithmuscle.com/images/full/2526619.jpg",
+
+    "comments" : [],
+    "date"     : "dt:2025-05-21 20:01:03",
+    "extension": "jpg",
+    "filename" : "2526619",
+    "id"       : "2526619",
+    "is_favorite": None,
+    "model"    : "Vladislava Galagan",
+    "model_list" : [
+        "Vladislava Galagan"
+    ],
+    "score"    : range(190, 250),
+    "source_filename": "",
+    "type"     : "picture",
+    "uploader" : "mrt",
+    "tags": [
+        "delts/shoulders",
+        "abs",
+        "casual",
+        "triceps",
+        "traps",
+        "bikini/competition suit",
+        "white",
+        "figure/fitness",
+        "bodybuilder",
+        "slavic",
+        "women's physique",
+        "russian",
+    ],
+},
+
+{
+    "#url"     : "https://www.girlswithmuscle.com/images/?name=Harmony%20Doughty",
+    "#category": ("", "girlswithmuscle", "search"),
+    "#class"   : girlswithmuscle.GirlswithmuscleSearchExtractor,
+    "#pattern" : girlswithmuscle.GirlswithmusclePostExtractor.pattern,
+    "#count"   : range(130, 150),
+},
+
+)