classfile,passes: model Nest attributes as IR (fix ClassFormatError)

NestHost/NestMembers were carried as Attribute::Raw with constant-pool
indices baked in. During writing the pool is rebuilt in a different order,
so those indices pointed at the wrong entries and the JVM rejected the
class: ClassFormatError: Nest member/host class_info_index N has bad
constant type.

Model them explicitly in the IR, convert on parse and write (resolving
class names through the new pool), and remap their class names during
rename. Add a NestMembers round-trip regression test. Verified on a real
jar: all Nest ClassFormatErrors gone.

crates/noxis-classfile/src/model/mod.rs

@@ -19,6 +19,10 @@ pub enum Attribute {
     Deprecated,
     Synthetic,
     InnerClasses(Vec<InnerClass>),
+    /// `NestHost`: класс, служащий nest-хостом (JVMS §4.7.28).
+    NestHost(String),
+    /// `NestMembers`: классы-члены этого nest-хоста (JVMS §4.7.29).
+    NestMembers(Vec<String>),
     /// `ConstantValue` поля (`static final`): значение из пула.
     ConstantValue(Const),
     /// `BootstrapMethods` для `invokedynamic` (лямбды): метод + аргументы.