added resository protocol, endpoint, api error and endpoint test

Stream-iOS/Stream-iOS/Core/Networking/APIError.swift

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+//
+//  APIError.swift
+//  Stream-iOS
+//
+//  Created by Ullash Podder on 14/07/2026.
+//
+
+import Foundation
+enum APIError: Error, Equatable {
+    case invalidResponse
+    case httpStatus(Int)
+    case decodingFailed
+}

Stream-iOS/Stream-iOS/Core/Networking/CharacterRepository.swift

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+//
+//  CharacterRepository.swift
+//  Stream-iOS
+//
+//  Created by Ullash Podder on 14/07/2026.
+//
+
+protocol CharacterRepository: Sendable {
+    func fetchCharacters(page: Int) async throws -> PagedResponse<CharacterDTO>
+}

Stream-iOS/Stream-iOS/Core/Networking/Endpoint.swift

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+//
+//  Endpoint.swift
+//  Stream-iOS
+//
+//  Created by Ullash Podder on 14/07/2026.
+//
+
+import Foundation
+
+struct Endpoint{
+    let path : String
+    let queryItems : [URLQueryItem]
+    var url:URL? {
+        var components = URLComponents()
+        components.scheme = "https"
+        components.host = "rickandmortyapi.com"
+        components.path = "/api" + path
+        components.queryItems = queryItems.isEmpty ? nil : queryItems
+        return components.url
+    }
+}
+extension Endpoint {
+    static func characters(page:Int) -> Endpoint{
+        Endpoint(path: "/character", queryItems: [URLQueryItem(name: "page", value: "\(page)")])
+    }
+}

Stream-iOS/Stream-iOS/Core/Networking/URLSessionCharacterRepository.swift

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+//
+//  URLSessionCharacterRepository.swift
+//  Stream-iOS
+//
+//  Created by Ullash Podder on 14/07/2026.
+//
+
+import Foundation

Stream-iOS/Stream-iOSTests/EndpointTests.swift

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+//
+//  EndpointTests.swift
+//  Stream-iOS
+//
+//  Created by Ullash Podder on 14/07/2026.
+//
+import Testing
+import Foundation
+@testable import Stream_iOS
+
+struct EndpointTests {
+    @Test func buildsCharacterPageURL() throws {   // <- throws here
+        let url = try #require(Endpoint.characters(page: 3).url)
+        #expect(url.absoluteString == "https://rickandmortyapi.com/api/character?page=3")
+    }
+}

Stream-iOS/Stream-iOSTests/Mocks/MockCharacterRepository.swift

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+//
+//  MockCharacterRepository.swift
+//  Stream-iOS
+//
+//  Created by Ullash Podder on 14/07/2026.
+//
+//import Testing
+//import Foundation
+@testable import Stream_iOS
+
+final class MockCharacterRepository: CharacterRepository, @unchecked Sendable {
+    var result: Result<PagedResponse<CharacterDTO>, Error> = .failure(APIError.invalidResponse)
+    private(set) var requestedPages: [Int] = []
+
+    func fetchCharacters(page: Int) async throws -> PagedResponse<CharacterDTO> {
+        requestedPages.append(page)
+        return try result.get()
+    }
+}