Revert "Exclude environment from CodingKeys"

This reverts commit 413a5c9.

Sources/ScipioKit/BuildOptions.swift

@@ -3,18 +3,6 @@ import OrderedCollections
 import Basics
 
 struct BuildOptions: Hashable, Codable, Sendable {
-
-    private enum CodingKeys: CodingKey {
-        case buildConfiguration
-        case isDebugSymbolsEmbedded
-        case frameworkType
-        case sdks
-        case extraFlags
-        case extraBuildParameters
-        case enableLibraryEvolution
-        case customFrameworkModuleMapContents
-    }
-
     init(
         buildConfiguration: BuildConfiguration,
         isDebugSymbolsEmbedded: Bool,
@@ -48,7 +36,7 @@ struct BuildOptions: Hashable, Codable, Sendable {
     /// - Note: It have to store the actual file contents rather than its path,
     /// because the cache key should change when the file contents change.
     let customFrameworkModuleMapContents: Data?
-    private(set) var environment: Environment? = nil
+    let environment: Environment?
 }
 
 public struct ExtraFlags: Hashable, Codable, Sendable {