Vendored swift-transformers: add Sendable to Hub.Repo and Hub.RepoType

Under Swift 6 strict concurrency, `Hub.RepoType` and `Hub.Repo` need `Sendable`
to cross actor/task boundaries; without it, builds that touch these types from
concurrent contexts fail. Both are trivially sendable — a `String`-raw enum and
an all-`let` struct of `Sendable` fields. Adds the conformance to the vendored
copy so vmlx-swift builds clean under Swift 6 without waiting on an upstream
swift-transformers release + vendor bump. No behavior change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: rcfa

Vendors/swift-transformers/Sources/Hub/Hub.swift

@@ -77,7 +77,7 @@ public extension Hub {
     }
 
     /// The type of repository on the Hugging Face Hub.
-    enum RepoType: String, Codable {
+    enum RepoType: String, Codable, Sendable {
         /// Model repositories containing machine learning models.
         case models
         /// Dataset repositories containing training and evaluation data.
@@ -90,7 +90,7 @@ public extension Hub {
     ///
     /// A repository is identified by its unique ID and type, allowing access to
     /// different kinds of resources hosted on the Hub platform.
-    struct Repo: Codable {
+    struct Repo: Codable, Sendable {
         /// The unique identifier for the repository (e.g., "microsoft/DialoGPT-medium").
         public let id: String
         /// The type of repository (models, datasets, or spaces).