refactor: Significantly refactor how conditions work internally (#1886)

- Much improved API cleanliness and testability to allow further
extensibility in future
 - Simplified code in `live` view

This technically contains a small change in how overrides work in the
`live` view. Since that change is _closer_ to the documentation, and
since this is likely to be rarely used, this is not considered a
breaking change. Previously, overrides for a given live camera would
always render _as if_ that camera was selected, vs was actually
selected. Now, overrides will only apply in the live view when the
camera is _actually_ selected. If this is an issue for you in practice,
lets discuss.

tests/conditions/state-manager.test.ts

@@ -0,0 +1,109 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { ConditionStateManager } from '../../src/conditions/state-manager';
+import { createStateEntity } from '../test-utils';
+
+describe('ConditionStateManager', () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it('should get state', () => {
+    const state = { fullscreen: true };
+
+    const manager = new ConditionStateManager();
+    manager.setState(state);
+    expect(manager.getState()).toEqual(state);
+  });
+
+  describe('should set state', () => {
+    it('should set and be able to get it again', () => {
+      const state = {
+        fullscreen: true,
+      };
+
+      const manager = new ConditionStateManager();
+
+      manager.setState(state);
+      expect(manager.getState()).toEqual(state);
+    });
+
+    it('should set but only trigger when necessary', () => {
+      const listener = vi.fn();
+      const manager = new ConditionStateManager();
+      manager.addListener(listener);
+
+      const state = {
+        fullscreen: true,
+      };
+
+      manager.setState(state);
+      expect(listener).toBeCalledTimes(1);
+
+      manager.setState(state);
+      expect(listener).toBeCalledTimes(1);
+
+      manager.setState({ ...state });
+      expect(listener).toBeCalledTimes(1);
+
+      manager.setState({
+        state: {
+          'binary_sensor.foo': createStateEntity(),
+        },
+      });
+      expect(listener).toBeCalledTimes(2);
+
+      manager.setState({ fullscreen: true });
+      expect(listener).toBeCalledTimes(2);
+
+      manager.setState({
+        state: {
+          'binary_sensor.foo': createStateEntity(),
+        },
+      });
+      expect(listener).toBeCalledTimes(2);
+
+      manager.setState({ fullscreen: false });
+      expect(listener).toBeCalledTimes(3);
+
+      manager.setState({ fullscreen: false });
+      expect(listener).toBeCalledTimes(3);
+
+      manager.setState({
+        state: {
+          'binary_sensor.foo': createStateEntity({ state: 'off' }),
+        },
+      });
+      expect(listener).toBeCalledTimes(4);
+    });
+  });
+
+  it('should add listener', () => {
+    const listener = vi.fn();
+    const manager = new ConditionStateManager();
+
+    manager.setState({ fullscreen: true });
+
+    manager.addListener(listener);
+
+    manager.setState({ expand: true });
+
+    expect(listener).toBeCalledWith({
+      old: { fullscreen: true },
+      change: { expand: true },
+      new: { fullscreen: true, expand: true },
+    });
+  });
+
+  it('should remove listener', () => {
+    const listener = vi.fn();
+    const manager = new ConditionStateManager();
+
+    manager.addListener(listener);
+    manager.removeListener(listener);
+
+    const state = { fullscreen: true };
+    manager.setState(state);
+
+    expect(listener).not.toBeCalled();
+  });
+});