[Doc] Update API doc and Sphinx version (#2346)

* Update Sphinx version to avoid regression in future doc update.

* Add missing IOS18 ops into API doc source.

Author: junpeiz

docs/source/coremltools.converters.mil.mil.ops.defs.rst

@@ -48,7 +48,7 @@ classify
 
    .. autoclass:: classify
 
-constexpr_ops
+constexpr_ops (iOS 16+)
 ---------------------------------------------------
 
 .. automodule:: coremltools.converters.mil.mil.ops.defs.iOS16.constexpr_ops
@@ -58,6 +58,18 @@ constexpr_ops
    .. autoclass:: constexpr_lut_to_dense
    .. autoclass:: constexpr_sparse_to_dense
 
+constexpr_ops (iOS 18+)
+---------------------------------------------------------------------
+
+.. automodule:: coremltools.converters.mil.mil.ops.defs.iOS18.compression
+
+   .. autoclass:: constexpr_blockwise_shift_scale
+   .. autoclass:: constexpr_lut_to_dense
+   .. autoclass:: constexpr_sparse_to_dense
+   .. autoclass:: constexpr_lut_to_sparse
+   .. autoclass:: constexpr_sparse_blockwise_shift_scale
+   .. autoclass:: constexpr_cast
+
 control\_flow
 ------------------------------------------------------------
 
@@ -281,6 +293,14 @@ recurrent (iOS 17+)
    .. autoclass:: lstm
    .. autoclass:: rnn
 
+recurrent (iOS 18+)
+--------------------------------------------------------
+
+.. automodule:: coremltools.converters.mil.mil.ops.defs.iOS18.recurrent
+
+   .. autoclass:: gru
+
+
 reduction (iOS 15+)
 --------------------------------------------------------
 

reqs/docs.pip

@@ -1,7 +1,7 @@
 Babel
 MarkupSafe
 Pygments
-Sphinx==7.3.1
+Sphinx==7.4.7
 alabaster
 certifi
 chardet