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/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;
+    }
   }
 
   /**