State byte markers can overwrite user dictionaries

### Feature Summary

State deserialization treats any user dictionary whose internal type marker equals bytes as Texera's byte envelope. Ordinary user state can therefore be converted into bytes and lose additional fields during a JSON round trip.

Before: user dictionary with reserved-looking keys -> decoded as bytes and fields are lost

After: user dictionary with marker key -> escaped dictionary envelope -> original mapping is restored

Reproduction evidence:

Round-trip nested state containing the keys __texera_type__, payload, and owner, with the type value set to bytes.

Version and commit evidence:

1.3.0-incubating-SNAPSHOT (main)

**Commit Hash**

70c21145887920528d7d5540e3fb790b43e8b759

**What browsers are you seeing the problem on?**

Not browser-specific.

**Relevant log output**

```text
decoded= {'config': b'hello'}
round_trip_equal= False
```

### Proposed Solution or Design

After: user dictionary with marker key -> escaped dictionary envelope -> original mapping is restored

### Affected Area

Workflow Engine (Amber)