fetch.swift

	func fetch<Result: Codable>(_ endpoint: Endpoint<Result>, cacheBehavior: CacheBehavior = .cacheElseNetwork) async throws -> Result {
		switch cacheBehavior {
		case .cacheElseNetwork:
			if let cached = self.cache[endpoint.cacheKey] {
				return cached.payload
			} else {
				return try await self.networkFetch(endpoint)
			}
		case .networkOnly:
			return try await self.networkFetch(endpoint)
		case .cacheOnly:
			if let cached = self.cache[endpoint.cacheKey] {
				return cached.payload
			} else {
				throw Error.cacheMiss
			}
		}
	}