feat: Add video message part type support for Alibaba Cloud vision models

[ding-ding666]

Summary

This PR adds support for a new video message part type in the eino schema to enable direct video frame transmission compatible with Alibaba Cloud's vision model services.

Background

Alibaba Cloud's Model Studio vision models support video content processing through a specific format that requires video frames to be sent as an array of base64-encoded images. This enhancement enables eino framework to work seamlessly with Alibaba Cloud's multimodal capabilities.

Reference: https://help.aliyun.com/zh/model-studio/vision#80dbf6ca8fh6s

Changes

• Added ChatMessagePartTypeVideo = "video" constant for video message parts
• Added ChatMessageVideo struct to handle video frames with base64-encoded data
• Updated ChatMessagePart struct to include Video *ChatMessageVideo field
• Updated message concatenation logic to handle video fields

API Changes

New Types

// ChatMessagePartTypeVideo represents video content with multiple frames
const ChatMessagePartTypeVideo ChatMessagePartType = "video"

// ChatMessageVideo handles video frames in base64 format for Alibaba Cloud compatibility
type ChatMessageVideo struct {
    Video    []string          `json:"video,omitempty"`    // Array of base64-encoded frames
    MIMEType string            `json:"mime_type,omitempty"` // Frame format (e.g., "image/jpeg")
    Extra    map[string]any    `json:"extra,omitempty"`     // Additional metadata
}

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[ding-ding666]

The following three links are a set of modifications:

#254
meguminnnnnnnnn/go-openai#3
cloudwego/eino-ext#280