Feature Request: Connection suggestions for flexible input types (AnyType/*)

## Problem

Custom nodes that use flexible input types (AnyType with `*`) cannot provide connection suggestions to users. When dragging from outputs or to inputs of AnyType, ComfyUI shows no compatible node suggestions, making workflows harder to build.

## Current Situation

**AnyType approach:**
```python
class AnyType(str):
def __ne__(self, __value: object) -> bool:
return False

any_typ = AnyType("*")

# In INPUT_TYPES:
"flexible_input": (any_typ, {"tooltip": "Accepts multiple types"})
```

**Result:** Accepts any connection but provides zero suggestions when dragging connections.

## Use Case

We have emotion control nodes that output `EMOTION_CONTROL` type, but our TTS engine needs to accept:
- `EMOTION_CONTROL` (from emotion vector nodes)
- `AUDIO` (direct audio emotion references)
- `NARRATOR_VOICE` (from character voice nodes)

Currently we must choose between:
1. **Flexible connections** (AnyType) = no suggestions
2. **Connection suggestions** (single type) = no flexibility
3. **Multiple types** `["TYPE1", "TYPE2"]` = creates dropdown widget, not input

## Proposed Solutions

**Option 1: Union Types**
```python
"flexible_input": (("EMOTION_CONTROL", "AUDIO", "NARRATOR_VOICE"), {...})
```

**Option 2: Enhanced AnyType**
```python
"flexible_input": (any_typ, {
"compatible_types": ["EMOTION_CONTROL", "AUDIO", "NARRATOR_VOICE"],
"tooltip": "..."
})
```

**Option 3: Connection Metadata**
Allow AnyType inputs to declare compatible types for suggestion purposes while maintaining runtime flexibility.

## Impact

This affects every custom node pack that needs flexible inputs:
- TTS engines accepting multiple emotion formats
- Image processors accepting various input types
- Universal converter nodes
- Workflow utility nodes

Currently all these nodes provide poor UX due to missing connection suggestions.

## Workaround

None that provides both flexibility and suggestions. AnyType is the current best practice but breaks discoverability.