community: Fix closed session in Infinity (#26933)

**Description:** 

The `aiohttp.ClientSession` is closed at the end of the with statement,
which causes an error during a second call.

The implemented fix is to define the session directly within the with
block, exactly like in the textembed code:


https://github.com/langchain-ai/langchain/blob/c6350d636e139bd9018f7225d3257c4be6139d54/libs/community/langchain_community/embeddings/textembed.py#L335-L346
 
**Issue:** Fix #26932

Co-authored-by: ccurme <chester.curme@gmail.com>

libs/community/langchain_community/embeddings/infinity.py

@@ -306,11 +306,9 @@ async def aembed(self, model: str, texts: List[str]) -> List[List[float]]:
         perm_texts_batched = self._batch(perm_texts)
 
         # Request
-        if self.aiosession is None:
-            self.aiosession = aiohttp.ClientSession(
-                trust_env=True, connector=aiohttp.TCPConnector(limit=32)
-            )
-        async with self.aiosession as session:
+        async with aiohttp.ClientSession(
+            trust_env=True, connector=aiohttp.TCPConnector(limit=32)
+        ) as session:
             embeddings_batch_perm = await asyncio.gather(
                 *[
                     self._async_request(