feat: add CreateOAuthTokenHandler factory to Brokerage base class

[Romazes]

Description

• Add AuthenticationFailed event to TokenHandler base class, raised when all retry attempts are exhausted after a failed token fetch
• Add protected CreateOAuthTokenHandler<TRequest, TResponse>() factory method to Brokerage base class that creates an OAuthTokenHandler and automatically subscribes to AuthenticationFailed, routing it to OnMessage(BrokerageMessageType.Error) to trigger graceful Lean shutdown

Related PRs

• https://github.com/QuantConnect/Lean.Brokerages.CharlesSchwab/pull/81

Related Issue

Motivation and Context

When a live brokerage fails to refresh its OAuth access token (e.g. "Error refreshing access token."), the error was only logged and the algorithm continued running in a broken state. The root cause is that OAuthTokenHandler.GetAccessToken throws an InvalidOperationException which propagates through the HTTP stack but never reaches Lean's shutdown mechanism.

This change introduces a single centralized point - Brokerage.CreateOAuthTokenHandler - where the wiring between OAuth failure and Lean termination is defined. Individual brokerage implementations pass this factory when constructing their API clients; no per-brokerage error handling logic is needed.

Requires Documentation Change

No

How Has This Been Tested?

• Solution builds with no errors
• Verified the shutdown path: AuthenticationFailed event => OnMessage(BrokerageMessageType.Error) => DefaultBrokerageMessageHandler => algorithm.SetRuntimeError() => graceful Engine shutdown

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Refactor (non-breaking change which improves implementation)
• Performance (non-breaking change which improves performance. Please add associated performance test and results)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Non-functional change (xml comments/documentation/etc)

Checklist:

• My code follows the code style of this project.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My branch follows the naming convention bug-<issue#>-<description> or feature-<issue#>-<description>