Add docstring for the flyweight factory function

src/types.jl

@@ -341,6 +341,25 @@ end
 ### Constructors
 ###
 
+"""
+$(TYPEDSIGNATURES)
+
+Implements hash consing (flyweight design pattern) for `BasicSymbolic` objects.
+
+This function checks if an equivalent `BasicSymbolic` object already exists based on a 
+custom hash (`hash2`) and equality check (`isequal2`) that incorporate metadata and 
+symtypes. If an equivalent object is found in the `wvd` (a `WeakValueDict`), the existing 
+object is returned. Otherwise, the input `s` is returned. This approach reduces memory 
+usage, improves compilation time for runtime code generation, and supports built-in common 
+subexpression elimination, especially beneficial when dealing with duplicate symbolic 
+expressions.
+
+Using a `WeakValueDict` ensures that only weak references to `BasicSymbolic` objects are 
+stored, allowing objects that are no longer strongly referenced to be garbage collected. 
+The custom `hash2` and `isequal2` functions are used instead of `Base.hash` and 
+`Base.isequal` respectively to avoid breaking existing tests that rely on the default 
+behavior of these functions, which does not consider metadata.
+"""
 function BasicSymbolic(s::BasicSymbolic)::BasicSymbolic
     h = hash2(s)
     t = get!(wvd, h, s)