Remove NonisolatedNonsendingByDefault feature flag due to Hummingbird incompatibility

[Copilot]

The NonisolatedNonsendingByDefault feature flag causes type mismatches with Hummingbird's middleware protocol. This flag implicitly annotates closure parameters as nonisolated(nonsending), but Hummingbird v2.17.0's MiddlewareProtocol expects plain closure types.

Changes

• Removed .enableUpcomingFeature("NonisolatedNonsendingByDefault") from Package.swift
• Retained other Swift 6 upcoming features (ExistentialAny, InternalImportsByDefault, MemberImportVisibility, InferIsolatedConformances, ImmutableWeakCaptures)

Error Context

// Protocol definition in Hummingbird
func handle(_ input: Input, context: Context, next: (Input, Context) async throws -> Output) async throws -> Output

// With NonisolatedNonsendingByDefault enabled, implementations get implicit annotation
func handle(_ request: Request, context: Context, next: nonisolated(nonsending) (Request, Context) async throws -> Response) async throws -> Response
// ❌ Type mismatch

The feature can be re-enabled once Hummingbird adds support for it.

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[Copilot]

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[zunda-pixel]

@copilot
NonisolatedNonsendingByDefaultを削除せずに対応する場合、Swift OpenAPI Hummingbirdを修正する必要がありますか？

[Copilot]

@copilot
NonisolatedNonsendingByDefaultを削除せずに対応する場合、Swift OpenAPI Hummingbirdを修正する必要がありますか？

いいえ、修正が必要なのは Hummingbird です。Swift OpenAPI Hummingbirdではありません。

エラーが発生していたのは、このプロジェクトで定義されている3つのミドルウェア（OpenAPIRequestContextMiddleware、RateLimitMiddleware、UserTokenMiddleware）が、Hummingbirdの RouterMiddleware プロトコルに準拠しているためです。

NonisolatedNonsendingByDefault を削除せずに対応する場合、Hummingbird本体（現在v2.17.0）がこの機能フラグをサポートする必要があります。Hummingbirdのリポジトリに機能リクエストを出すか、PRを送ることで対応できます。

ただし、Swift OpenAPI Hummingbirdを含む他の依存関係も同じ問題を抱えている可能性があるため、エコシステム全体が対応するまで待つ必要があるかもしれません。