feat: Phase 9.78e complete - instance_v2 migration with legacy compatibility

- instance_v2 now includes legacy compatibility layer
- All interpreter code migrated to use instance_v2
- Added legacy field access methods (get_fields, set_field_legacy, etc.)
- Fixed type conversion issues (NyashValue vs SharedNyashBox)
- instance.rs still exists but no longer used in interpreter
- TODO: Remove instance.rs completely in next phase
- TODO: Implement proper SharedNyashBox -> NyashValue conversion

🤖 Generated with [Claude Code](https://claude.ai/code)

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

src/interpreter/expressions/calls.rs

@@ -9,7 +9,7 @@ use crate::boxes::{ArrayBox, FloatBox, MapBox, FutureBox};
 use crate::boxes::{BufferBox, JSONBox, HttpClientBox, StreamBox, RegexBox, IntentBox, SocketBox};
 use crate::boxes::{HTTPServerBox, HTTPRequestBox, HTTPResponseBox, MathBox, TimeBox, DateTimeBox};
 use crate::boxes::{RandomBox, SoundBox, DebugBox};
-use crate::instance::InstanceBox;
+use crate::instance_v2::InstanceBox;
 use crate::channel_box::ChannelBox;
 use crate::interpreter::core::{NyashInterpreter, RuntimeError};
 use crate::interpreter::finalization;