[Doc] Convert docs to use colon fences (#12471)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/source/api/engine/index.md

@@ -8,10 +8,10 @@
 .. currentmodule:: vllm.engine
 ```
 
-```{toctree}
+:::{toctree}
 :caption: Engines
 :maxdepth: 2
 
 llm_engine
 async_llm_engine
-```
+:::

docs/source/api/model/index.md

@@ -2,10 +2,10 @@
 
 ## Submodules
 
-```{toctree}
+:::{toctree}
 :maxdepth: 1
 
 interfaces_base
 interfaces
 adapters
-```
+:::

docs/source/api/multimodal/index.md

@@ -17,7 +17,7 @@ Looking to add your own multi-modal model? Please follow the instructions listed
 
 ## Submodules
 
-```{toctree}
+:::{toctree}
 :maxdepth: 1
 
 inputs
@@ -25,4 +25,4 @@ parse
 processing
 profiling
 registry
-```
+:::

docs/source/api/offline_inference/index.md

@@ -1,9 +1,9 @@
 # Offline Inference
 
-```{toctree}
+:::{toctree}
 :caption: Contents
 :maxdepth: 1
 
 llm
 llm_inputs
-```
+:::