Add Promise.Race, Promise.Any, Promise.AllSettled, Cancellation, Timeout, and Finally support

[JavierusTk]

Summary

This PR extends the Delphi Promises library with several combinators and features commonly found in modern promise implementations (JavaScript/TypeScript):

• Promise.Race<T> — Resolves/rejects as soon as the first promise settles
• Promise.Any<T> — Resolves with the first fulfilled promise; rejects only if all fail (raises EAggregatePromiseError)
• Promise.AllSettled<T> — Waits for all promises to settle, returning results with status (fulfilled/rejected) without short-circuiting on errors
• Promise.Timeout<T> — Wraps a promise with a deadline; raises EPromiseTimeout if not settled in time
• Cancellation — Cooperative cancellation via ICancellationToken / TCancellationTokenSource; raises EPromiseCancelled
• Finally — Executes a callback when the promise settles regardless of outcome (resolved or rejected)

New files

File	Purpose
Core/Types/Next.Core.Promises.Cancellation.pas	ICancellationToken, TCancellationTokenSource
Core/Types/Next.Core.Promises.Exceptions.pas	EPromiseException hierarchy (EPromiseTimeout, EPromiseCancelled, EAggregatePromiseError)
Test/Types/TestPromiseRace.pas	7 test cases for Race
Test/Types/TestPromiseAny.pas	5 test cases for Any
Test/Types/TestPromiseAllSettled.pas	6 test cases for AllSettled
Test/Types/TestPromiseCancellation.pas	8 test cases for Cancellation
Test/Types/TestPromiseTimeout.pas	3 test cases for Timeout
Test/Types/TestPromiseFinally.pas	4 test cases for Finally
Test/Types/TestPromiseExceptions.pas	4 test cases for exception types

Changes to existing files

• Next.Core.Promises.pas — Added Race, Any, AllSettled, Timeout, Finally, and cancellation-aware execution to TPromise<T>
• readme.md — Comprehensive documentation for all new features with usage examples
• TestNext.dpr / TestNext.dproj — Registered new test units

Test plan

• All 37+ new test cases pass (Race, Any, AllSettled, Cancellation, Timeout, Finally, Exceptions)
• Existing tests continue to pass
• Verify on Delphi 10.x+ (developed on Delphi 12)

Design notes

• Non-breaking: All additions are new methods/types; no existing API signatures were changed
• Cooperative cancellation: Follows the cancellation token pattern — promises check the token and raise EPromiseCancelled rather than being forcefully
  terminated
• Exception hierarchy: All new exceptions inherit from EPromiseException for easy catch filtering
• AllSettled result type: Uses TPromiseResult<T> record with Status (fulfilled/rejected), Value, and ErrorMessage fields