[Misc] Streamline unique id generation (#29375)

Signed-off-by: Nick Hill <nhill@redhat.com>

vllm/utils/__init__.py

@@ -52,9 +52,11 @@ STR_FLASHINFER_ATTN_VAL: str = "FLASHINFER"
 STR_FLASH_ATTN_VAL: str = "FLASH_ATTN"
 STR_INVALID_VAL: str = "INVALID"
 
+MASK_64_BITS = (1 << 64) - 1
+
 
 def random_uuid() -> str:
-    return str(uuid.uuid4().hex)
+    return f"{uuid.uuid4().int & MASK_64_BITS:016x}"  # 16 hex chars
 
 
 def length_from_prompt_token_ids_or_embeds(