refactor(deps): demote LangChain and LangChain-providers from core to dev

Now that DefaultFramework handles OpenAI-compatible chat via httpx,
LangChain is no longer needed for basic operation. Moving it out of
core slims the mandatory install substantially and makes the
LangChain integration genuinely opt-in.

Core dependencies (removed):
- langchain, langchain-core, langchain-community: only imported lazily
  inside nemoguardrails/integrations/langchain/ and in conditional
  paths in llm/frameworks.py and rails/llm/llmrails.py (raw-LangChain-
  LLM path).
- langchain-openai: not imported anywhere in src; only referenced by
  test skipif guards.
- langchain-nvidia-ai-endpoints: imported conditionally in
  embeddings/providers/nim.py (NIM embeddings) and in LangChain-NIM
  adapter. Users who need these paths install the package directly.

Extras (removed):
- openai (was -> langchain-openai): obsolete, DefaultFramework uses
  httpx directly.
- nvidia (was -> langchain-nvidia-ai-endpoints): obsolete for chat;
  NIM embeddings users should install langchain-nvidia-ai-endpoints
  directly.

Extras (kept and adjusted):
- server: still includes openai because server/schemas and server/api
  import openai.types.chat at module scope (server won't start
  without the openai SDK).
- all: updated to drop the removed extras.

Dev group additions:
- langchain, langchain-core, langchain-community: needed by the
  LangChain integration tests under tests/integrations/langchain/.
- langchain-openai, langchain-nvidia-ai-endpoints: skip-guarded by
  tests today; installed in dev so those guards activate.

Runtime behavior unchanged: code that used these packages always
imported them lazily or conditionally. Users on
NEMOGUARDRAILS_LLM_FRAMEWORK=langchain now need to install
langchain-* themselves; an upgrade note in the migration guide is
appropriate (follow-up).

Author: Pouyanpi

poetry.lock

@@ -58,9 +58,6 @@ onnxruntime = [
 ]
 httpx = ">=0.24.1"
 jinja2 = ">=3.1.6"
-langchain = ">=0.2.14,<2.0.0"
-langchain-core = ">=0.2.14,<2.0.0"
-langchain-community = ">=0.2.5,<2.0.0"
 lark = ">=1.1.7"
 nest-asyncio = ">=1.5.6,"
 # NOTE:
@@ -77,15 +74,14 @@ starlette = ">=0.49.1"
 typer = ">=0.8"
 uvicorn = ">=0.23"
 watchdog = ">=3.0.0,"
+
+# server (openai SDK types used by server/schemas and server/api)
 openai = { version = ">=1.0.0,<3.0.0", optional = true }
 
 # tracing
 opentelemetry-api = { version = ">=1.27.0,<2.0.0", optional = true }
 aiofiles = { version = ">=24.1.0", optional = true }
 
-# openai
-langchain-openai = { version = ">=0.1.0", optional = true }
-
 # eval
 tqdm = { version = ">=4.65,<5.0", optional = true }
 streamlit = { version = "^1.37.0", optional = true, python = ">=3.10,<3.14" }
@@ -103,9 +99,6 @@ numpy = [
 presidio-analyzer = { version = ">=2.2", optional = true, python = "<3.13" }
 presidio-anonymizer = { version = ">=2.2", optional = true, python = "<3.13" }
 
-# nim
-langchain-nvidia-ai-endpoints = { version = ">= 0.2.0", optional = true }
-
 # gpc
 google-cloud-language = { version = ">=2.14.0", optional = true }
 
@@ -118,10 +111,8 @@ fast-langdetect = { version = ">=1.0.0", optional = true }
 [tool.poetry.extras]
 sdd = ["presidio-analyzer", "presidio-anonymizer"]
 eval = ["tqdm", "numpy", "streamlit", "tornado"]
-openai = ["langchain-openai"]
 gcp = ["google-cloud-language"]
 tracing = ["opentelemetry-api", "aiofiles"]
-nvidia = ["langchain-nvidia-ai-endpoints"]
 jailbreak = ["yara-python"]
 multilingual = ["fast-langdetect"]
 server = ["aiofiles", "openai"]
@@ -134,12 +125,10 @@ all = [
   "tqdm",
   "numpy",
   "streamlit",
-  "langchain-openai",
   "openai",
   "google-cloud-language",
   "opentelemetry-api",
   "aiofiles",
-  "langchain-nvidia-ai-endpoints",
   "yara-python",
   "fast-langdetect",
 ]
@@ -165,6 +154,13 @@ fast-langdetect = ">=1.0.0"
 openai = ">=1.0.0,<3.0.0"
 pyright = "^1.1.405"
 ruff = "0.14.6"
+# LangChain integration is now opt-in at runtime (DefaultFramework replaces it for chat).
+# These dev deps keep the LangChain-specific tests and the NIM embeddings test path working.
+langchain = ">=0.2.14,<2.0.0"
+langchain-core = ">=0.2.14,<2.0.0"
+langchain-community = ">=0.2.5,<2.0.0"
+langchain-openai = ">=0.1.0"
+langchain-nvidia-ai-endpoints = ">=0.2.0"
 
 # Directories in which to run Pyright type-checking
 [tool.pyright]