langchain_core: add file_type option to make file type default as png (#27855)

Thank you for contributing to LangChain!

- [ ] **PR title**: "package: description"
- Where "package" is whichever of langchain, community, core, etc. is
being modified. Use "docs: ..." for purely docs changes, "templates:
..." for template changes, "infra: ..." for CI changes.
  - Example: "community: add foobar LLM"

- [ ] **description**
langchain_core.runnables.graph_mermaid.draw_mermaid_png calls this
function, but the Mermaid API returns JPEG by default. To be consistent,
add the option `file_type` with the default `png` type.

- [ ] **Add tests and docs**: If you're adding a new integration, please
include
With this small change, I didn't add tests and docs.

- [ ] **Lint and test**: Run `make format`, `make lint` and `make test`
from the root of the package(s) you've modified. See contribution
guidelines for more:
One long sentence was divided into two.

Additional guidelines:
- Make sure optional dependencies are imported within a function.
- Please do not add dependencies to pyproject.toml files (even optional
ones) unless they are required for unit tests.
- Most PRs should not touch more than one package.
- Changes should be backwards compatible.
- If you are adding something to community, do not re-import it in
langchain.

If no one reviews your PR within a few days, please @-mention one of
baskaryan, efriis, eyurtsev, ccurme, vbarda, hwchase17.

libs/core/langchain_core/runnables/graph_mermaid.py

@@ -2,7 +2,7 @@ import asyncio
 import base64
 import re
 from dataclasses import asdict
-from typing import Optional
+from typing import Literal, Optional
 
 from langchain_core.runnables.graph import (
     CurveStyle,
@@ -306,6 +306,7 @@ def _render_mermaid_using_api(
     mermaid_syntax: str,
     output_file_path: Optional[str] = None,
     background_color: Optional[str] = "white",
+    file_type: Optional[Literal["jpeg", "png", "webp"]] = "png",
 ) -> bytes:
     """Renders Mermaid graph using the Mermaid.INK API."""
     try:
@@ -329,7 +330,8 @@ def _render_mermaid_using_api(
             background_color = f"!{background_color}"
 
     image_url = (
-        f"https://mermaid.ink/img/{mermaid_syntax_encoded}?bgColor={background_color}"
+        f"https://mermaid.ink/img/{mermaid_syntax_encoded}"
+        f"?type={file_type}&bgColor={background_color}"
     )
     response = requests.get(image_url, timeout=10)
     if response.status_code == 200: