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/buffer/Constants.ts

@@ -147,11 +147,4 @@ export const enum ExtFlags {
   VARIANT_OFFSET = 0xE0000000
 }
 
-export const enum UnderlineStyle {
-  NONE = 0,
-  SINGLE = 1,
-  DOUBLE = 2,
-  CURLY = 3,
-  DOTTED = 4,
-  DASHED = 5
-}
+export { UnderlineStyle } from '../Types';

src/common/buffer/Types.ts

@@ -3,54 +3,7 @@
  * @license MIT
  */
 
-import { IAttributeData, ICircularList, IBufferLine, ICellData, IMarker, ICharset, IDisposable } from '../Types';
-import type { IEvent } from '../Event';
+export type { IBuffer, IBufferSet } from '../Types';
 
 // BufferIndex denotes a position in the buffer: [rowIndex, colIndex]
 export type BufferIndex = [number, number];
-
-export interface IBuffer {
-  readonly lines: ICircularList<IBufferLine>;
-  ydisp: number;
-  ybase: number;
-  y: number;
-  x: number;
-  tabs: any;
-  scrollBottom: number;
-  scrollTop: number;
-  hasScrollback: boolean;
-  savedY: number;
-  savedX: number;
-  savedCharset: ICharset | undefined;
-  savedCharsets: (ICharset | undefined)[];
-  savedGlevel: number;
-  savedOriginMode: boolean;
-  savedWraparoundMode: boolean;
-  savedCurAttrData: IAttributeData;
-  isCursorInViewport: boolean;
-  markers: IMarker[];
-  translateBufferLineToString(lineIndex: number, trimRight: boolean, startCol?: number, endCol?: number): string;
-  getWrappedRangeForLine(y: number): { first: number, last: number };
-  nextStop(x?: number): number;
-  prevStop(x?: number): number;
-  getBlankLine(attr: IAttributeData, isWrapped?: boolean): IBufferLine;
-  getNullCell(attr?: IAttributeData): ICellData;
-  getWhitespaceCell(attr?: IAttributeData): ICellData;
-  addMarker(y: number): IMarker;
-  clearMarkers(y: number): void;
-  clearAllMarkers(): void;
-}
-
-export interface IBufferSet extends IDisposable {
-  alt: IBuffer;
-  normal: IBuffer;
-  active: IBuffer;
-
-  onBufferActivate: IEvent<{ activeBuffer: IBuffer, inactiveBuffer: IBuffer }>;
-
-  activateNormalBuffer(): void;
-  activateAltBuffer(fillAttr?: IAttributeData): void;
-  reset(): void;
-  resize(newCols: number, newRows: number): void;
-  setupTabStops(i?: number): void;
-}