Replace the broken test suite with working GdUnit4 tests

The previous tests never compiled: they used GUT's assert functions,
Godot 3 APIs and reassigned autoload functions, so no test ran.

- 90 tests: unit tests for the playlist, songs, player scoring, time
  formatting, search and the server client, plus integration tests
  that run MainWindow and SyncWindow against a fake server
- Keybind tests check that Alt+<number> and Ctrl+Alt+<number> keep
  following the player rows while players are added and removed
- run_tests.sh finds Godot and runs the suite headless (~10 seconds)
- CI runs the tests before the build job in gitea-build.yaml; the
  separate test.yml used a GitHub action that does not exist
- GdUnit4 is committed instead of ignored, since the project enables
  it, and .gitea/ is no longer ignored
- Exported builds leave out tests/ and addons/gdUnit4/

addons/gdUnit4/src/update/GdUnitPatcher.gd

@@ -0,0 +1,75 @@
+class_name GdUnitPatcher
+extends RefCounted
+
+
+const _base_dir := "res://addons/gdUnit4/src/update/patches/"
+
+var _patches := Dictionary()
+
+
+func scan(current :GdUnit4Version) -> void:
+	_scan(_base_dir, current)
+
+
+func _scan(scan_path :String, current :GdUnit4Version) -> void:
+	_patches = Dictionary()
+	var patch_paths := _collect_patch_versions(scan_path, current)
+	for path in patch_paths:
+		prints("scan for patches checked '%s'" % path)
+		_patches[path] = _scan_patches(path)
+
+
+func patch_count() -> int:
+	var count := 0
+	for key :String in _patches.keys():
+		@warning_ignore("unsafe_method_access")
+		count += _patches[key].size()
+	return count
+
+
+func execute() -> void:
+	for key :String in _patches.keys():
+		for path :String in _patches[key]:
+			var patch :GdUnitPatch = (load(key + "/" + path) as GDScript).new()
+			if patch:
+				prints("execute patch", patch.version(), patch.get_script().resource_path)
+				if not patch.execute():
+					prints("error checked execution patch %s" % key + "/" + path)
+
+
+func _collect_patch_versions(scan_path :String, current :GdUnit4Version) -> PackedStringArray:
+	if not DirAccess.dir_exists_absolute(scan_path):
+		return PackedStringArray()
+	var patches := Array()
+	var dir := DirAccess.open(scan_path)
+	if dir != null:
+		@warning_ignore("return_value_discarded")
+		dir.list_dir_begin() # TODO GODOT4 fill missing arguments https://github.com/godotengine/godot/pull/40547
+		var next := "."
+		while next != "":
+			next = dir.get_next()
+			if next.is_empty() or next == "." or next == "..":
+				continue
+			var version := GdUnit4Version.parse(next)
+			if version.is_greater(current):
+				patches.append(scan_path + next)
+	patches.sort()
+	return PackedStringArray(patches)
+
+
+func _scan_patches(path :String) -> PackedStringArray:
+	var patches := Array()
+	var dir := DirAccess.open(path)
+	if dir != null:
+		@warning_ignore("return_value_discarded")
+		dir.list_dir_begin() # TODOGODOT4 fill missing arguments https://github.com/godotengine/godot/pull/40547
+		var next := "."
+		while next != "":
+			next = dir.get_next()
+			# step over directory links and .uid files
+			if next.is_empty() or next == "." or next == ".." or next.ends_with(".uid"):
+				continue
+			patches.append(next)
+	# make sorted from lowest to high version
+	patches.sort()
+	return PackedStringArray(patches)