[skip ci] docs: Add docstrings for ZIP and YMatrix

Author: PMeira

dss/IYMatrix.py

@@ -7,6 +7,15 @@
 from typing import Tuple, List
 
 class IYMatrix(Base):
+    '''
+    YMatrix provides access to some lower-level solution aspects.
+
+    Part of this class is ported from the original OpenDSSDirect.DLL back in 2017, but 
+    part is new. Since this is not exposed in the official COM API, it is marked as an extension.
+
+    (**API Extension**)
+    '''
+    
     __slots__ = []
 
     def GetCompressedYMatrix(self, factor: bool = True) -> Tuple[ComplexArray, Int32Array, Int32Array]:

dss/IZIP.py

@@ -4,6 +4,17 @@
 from typing import AnyStr, Optional, List
 
 class IZIP(Base):
+    '''
+    ZIP allows controlling the ZIP-compressed file functions from AltDSS/DSS C-API.
+
+    It allows opening a ZIP file, and loading circuits directly from it, without requiring extracting the contents to files before reading.
+    
+    The implementation provides a specialization which allows more efficient access if the ZIP file is open and reused for many circuits. 
+    Doing so reduces the overhead of the initial opening and indexing of the file contents.
+
+    (**API Extension**)
+    '''
+
     __slots__ = []
 
     _columns = []