QdrantVectorStore.as_retriever(search_type="mmr") inverts lambda_mult semantics

### Submission checklist - [x] This is a bug, not a usage question. - [x] I added a clear and descriptive title that summarizes this issue. - [x] I used the GitHub search to find a similar question and didn't find it. - [x] I am sure that this is a bug in LangChain rather than my code. - [x] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package). - [x] This is not related to the langchain-community package. - [x] I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS. ### Package (Required) - [ ] langchain - [ ] langchain-openai - [ ] langchain-anthropic - [ ] langchain-classic - [ ] langchain-core - [ ] langchain-model-profiles - [ ] langchain-tests - [ ] langchain-text-splitters - [ ] langchain-chroma - [ ] langchain-deepseek - [ ] langchain-exa - [ ] langchain-fireworks - [ ] langchain-groq - [ ] langchain-huggingface - [ ] langchain-mistralai - [ ] langchain-nomic - [ ] langchain-ollama - [ ] langchain-openrouter - [ ] langchain-perplexity - [x] langchain-qdrant - [ ] langchain-xai - [ ] Other / not sure / general ### Related Issues / PRs _No response_ ### Reproduction Steps / Example Code (Python) ```python from dotenv import load_dotenv import os import numpy as np from langchain_groq import ChatGroq from langchain_core.documents import Document from langchain_core.output_parsers import StrOutputParser from langchain_qdrant import QdrantVectorStore from langchain_huggingface import HuggingFaceEmbeddings from qdrant_client import QdrantClient from qdrant_client.models import Distance, VectorParams load_dotenv() api_key = os.getenv("GROQ_API_KEY") model = ChatGroq( model="llama-3.3-70b-versatile", temperature=0.5, api_key=api_key, ) parser = StrOutputParser() embedding_model = HuggingFaceEmbeddings(model_name="BAAI/bge-small-en-v1.5") docs = [ # LangChain / RAG cluster (tight, on-topic) Document(page_content="LangChain makes it easy to wo…