experimental[patch]: update module doc strings (#19539)

Added missed module descriptions. Fixed format.

libs/experimental/langchain_experimental/cpal/__init__.py

@@ -0,0 +1,17 @@
+"""
+**Causal program-aided language (CPAL)** is a concept implemented in LangChain as
+a chain for causal modeling and narrative decomposition.
+
+CPAL improves upon the program-aided language (**PAL**) by incorporating
+causal structure to prevent hallucination in language models,
+particularly when dealing with complex narratives and math
+problems with nested dependencies.
+
+CPAL involves translating causal narratives into a stack of operations,
+setting hypothetical conditions for causal models, and decomposing
+narratives into story elements.
+
+It allows for the creation of causal chains that define the relationships
+between different elements in a narrative, enabling the modeling and analysis
+of causal relationships within a given context.
+"""