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/

tests/unit/test_search.gd

@@ -0,0 +1,62 @@
+extends GdUnitTestSuite
+
+const SearchWindowScript: GDScript = preload("res://SearchWindow.gd")
+
+var _search: Control
+
+
+func before_test() -> void:
+    _search = auto_free(SearchWindowScript.new())
+    _search.set_soundtracks([
+        "Chrono Trigger",
+        "Final Fantasy VI",
+        "Mario & Luigi: Superstar Saga",
+        "Pokémon Red",
+        "Q*bert",
+        "Super Mario 64",
+        "The Legend of Zelda: A Link to the Past",
+    ])
+
+
+func test_plain_text_matches_case_insensitively() -> void:
+    assert_array(_search.find_matches("chrono")).contains_exactly(["Chrono Trigger"])
+
+
+func test_contains_matches_come_before_letter_order_matches() -> void:
+    var matches: Array[String] = _search.find_matches("mario")
+
+    assert_array(matches).contains_exactly([
+        "Mario & Luigi: Superstar Saga",
+        "Super Mario 64",
+    ])
+
+
+func test_ignores_spaces() -> void:
+    assert_array(_search.find_matches("finalfantasy")).contains_exactly(["Final Fantasy VI"])
+
+
+func test_and_matches_ampersand() -> void:
+    assert_array(_search.find_matches("mario and luigi")).contains(["Mario & Luigi: Superstar Saga"])
+
+
+func test_accented_letters_match_plain_letters() -> void:
+    assert_array(_search.find_matches("pokemon")).contains_exactly(["Pokémon Red"])
+
+
+func test_letters_in_order_match_abbreviations() -> void:
+    assert_array(_search.find_matches("lozlttp")).contains_exactly([
+        "The Legend of Zelda: A Link to the Past",
+    ])
+
+
+func test_regex_characters_are_matched_literally() -> void:
+    assert_array(_search.find_matches("q*b")).contains_exactly(["Q*bert"])
+
+
+func test_no_matches() -> void:
+    assert_array(_search.find_matches("metroid")).is_empty()
+
+
+func test_clean_term() -> void:
+    assert_str(_search.clean_term("Rock 'n Roll Racing")).is_equal("rockandrollracing")
+    assert_str(_search.clean_term("Ys I & II")).is_equal("ysiandii")