Add unit tests for action value formatting and distribution

- Implemented a new test script `test_action_values.gd` to verify the precision of fractional action amounts and the distinctiveness of adjacent values.
- Added checks to ensure that action values are correctly formatted and that the distribution of actions preserves distinct requests.
- Included validation for rendered button labels to confirm they are distinguishable.

tests/test_action_values.gd

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+extends SceneTree
+
+var failures: int = 0
+var checks: int = 0
+
+func _initialize() -> void:
+    call_deferred("run")
+
+func check(value: bool, message: String) -> void:
+    checks += 1
+    if not value:
+        failures += 1
+        push_error(message)
+
+func run() -> void:
+    var actions = load("res://ui/actions/actions.tscn").instantiate()
+    root.add_child(actions)
+    var values: Array = [0.1, 0.01, 0.001, 1.0, 10.0]
+    var labels: Array = []
+    for value in values:
+        labels.append(actions._format_action_value(value))
+    check(labels == ["0.10", "0.010", "0.0010", "1", "10"], "Fractional action amounts retain precision")
+    check(labels[0] != labels[1] and labels[1] != labels[2], "Adjacent fractional amounts are distinguishable")
+    actions.set_actions("test", 123.0)
+    check(actions.action_values[0] == 1.0 and actions.action_values[1] == 10.0, "Distribution preserves distinct requests")
+    check(actions.action_labels[0].text != actions.action_labels[1].text, "Rendered adjacent buttons are distinct")
+    actions.queue_free()
+    print("Action values: %d checks, %d failures" % [checks, failures])
+    quit(0 if failures == 0 else 1)

tests/test_action_values.gd.uid

@@ -0,0 +1 @@
+uid://dilbcphuku6k1