feat: Improve embedding request handling and support across channels

- Update EmbeddingRequest DTO to support more flexible input types
- Add input parsing method to handle various input formats
- Implement ConvertEmbeddingRequest for multiple channel adaptors
- Remove relayMode parameter from EmbeddingHelper
- Add input validation for embedding requests
- Simplify embedding request conversion for different channels

relay/channel/baidu/relay-baidu.go

@@ -87,7 +87,7 @@ func streamResponseBaidu2OpenAI(baiduResponse *BaiduChatStreamResponse) *dto.Cha
 	return &response
 }
 
-func embeddingRequestOpenAI2Baidu(request dto.GeneralOpenAIRequest) *BaiduEmbeddingRequest {
+func embeddingRequestOpenAI2Baidu(request dto.EmbeddingRequest) *BaiduEmbeddingRequest {
 	return &BaiduEmbeddingRequest{
 		Input: request.ParseInput(),
 	}