Add oxlint import/no-cycle and break existing src/common cycles

Enable oxlint's import/no-cycle rule (import plugin) so circular module
dependencies are caught in CI, similar to eslint-plugin-import/no-cycle
and biome no-import-cycles discussed in the issue.

Relocate shared types and dependencies to remove cycles under src/common:

- Types.ts: host IInsertEvent, IDeleteEvent, IParams, UnderlineStyle,
  IBuffer, and IBufferSet; drop imports from CircularList, buffer/Types,
  parser/Types, and Services
- CoreTerminal.ts: define and export ICoreTerminal
- ServiceRegistry.ts: define IServiceIdentifier (break Services registry loop)
- UnicodeService: stop constructing UnicodeV6; CoreTerminal registers the
  default v6 provider after service creation
- buffer/Types.ts and parser/Types.ts: re-export moved types for callers

Fixes https://github.com/xtermjs/xterm.js/issues/5897

Co-authored-by: Cursor <cursoragent@cursor.com>

src/common/services/InstantiationService.ts

@@ -9,8 +9,8 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { IInstantiationService, IServiceIdentifier } from './Services';
-import { getServiceDependencies } from './ServiceRegistry';
+import { IInstantiationService } from './Services';
+import { IServiceIdentifier, getServiceDependencies } from './ServiceRegistry';
 
 export class ServiceCollection {
 

src/common/services/ServiceRegistry.ts

@@ -9,7 +9,11 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { IServiceIdentifier } from './Services';
+export interface IServiceIdentifier<T> {
+  (...args: any[]): void;
+  type: T;
+  _id: string;
+}
 
 const enum Constants {
   DI_TARGET = 'di$target',

src/common/services/Services.ts

@@ -6,7 +6,7 @@
 import type { IDecoration, IDecorationOptions, ILinkHandler, ILogger, IWindowsPty, IOverviewRulerOptions } from '@xterm/xterm';
 import { CoreMouseEncoding, CoreMouseEventType, CursorInactiveStyle, CursorStyle, IAttributeData, ICharset, IColor, ICoreMouseEvent, ICoreMouseProtocol, IDecPrivateModes, IDisposable, IKittyKeyboardState, IModes, IOscLinkData, IWindowOptions } from '../Types';
 import { IBuffer, IBufferSet } from '../buffer/Types';
-import { createDecorator } from './ServiceRegistry';
+import { createDecorator, IServiceIdentifier } from './ServiceRegistry';
 import type { Emitter, IEvent } from '../Event';
 
 export const IBufferService = createDecorator<IBufferService>('BufferService');
@@ -119,12 +119,6 @@ export interface ICharsetService {
   setgCharset(g: number, charset: ICharset | undefined): void;
 }
 
-export interface IServiceIdentifier<T> {
-  (...args: any[]): void;
-  type: T;
-  _id: string;
-}
-
 export interface IBrandedService {
   serviceBrand: undefined;
 }

src/common/services/UnicodeService.test.ts

@@ -4,6 +4,7 @@
  */
 
 import { assert } from 'chai';
+import { UnicodeV6 } from '../input/UnicodeV6';
 import { UnicodeService } from './UnicodeService';
 import { IUnicodeVersionProvider } from './Services';
 
@@ -21,6 +22,7 @@ describe('unicode provider', () => {
   let us: UnicodeService;
   beforeEach(() => {
     us = new UnicodeService();
+    us.register(new UnicodeV6());
   });
   it('default to V6', () => {
     assert.equal(us.activeVersion, '6');

src/common/services/UnicodeService.ts

@@ -3,7 +3,6 @@
  * @license MIT
  */
 
-import { UnicodeV6 } from '../input/UnicodeV6';
 import { IUnicodeService, IUnicodeVersionProvider, UnicodeCharProperties, UnicodeCharWidth } from './Services';
 import { Emitter } from '../Event';
 
@@ -12,7 +11,7 @@ export class UnicodeService implements IUnicodeService {
 
   private _providers: {[key: string]: IUnicodeVersionProvider} = Object.create(null);
   private _active: string = '';
-  private _activeProvider: IUnicodeVersionProvider;
+  private _activeProvider!: IUnicodeVersionProvider;
 
   private readonly _onChange = new Emitter<string>();
   public readonly onChange = this._onChange.event;
@@ -30,13 +29,6 @@ export class UnicodeService implements IUnicodeService {
     return ((state & 0xffffff) << 3) | ((width & 3) << 1) | (shouldJoin?1:0);
   }
 
-  constructor() {
-    const defaultProvider = new UnicodeV6();
-    this.register(defaultProvider);
-    this._active = defaultProvider.version;
-    this._activeProvider = defaultProvider;
-  }
-
   public dispose(): void {
     this._onChange.dispose();
   }
@@ -60,6 +52,9 @@ export class UnicodeService implements IUnicodeService {
 
   public register(provider: IUnicodeVersionProvider): void {
     this._providers[provider.version] = provider;
+    if (!this._active) {
+      this.activeVersion = provider.version;
+    }
   }
 
   /**