Chore: add docs and tests for decimal vectors (#5185)

Tracking Issue: #5028

Note that I'm probably going to move where this is placed in the next
[PR](#5186) but the content
will be the same.

Signed-off-by: Connor Tsui <[email protected]>

Author: connortsui20

vortex-vector/src/binaryview/types.rs

@@ -120,7 +120,8 @@ pub trait BinaryViewTypeUpcast {
 
 /// Private module to seal the `BinaryViewType` trait.
 mod private {
-    /// Sealed trait to prevent external implementations of [`VarBinType`].
+    /// Sealed trait to prevent external implementations of
+    /// [`BinaryViewType`](super::BinaryViewType).
     pub trait Sealed {}
 
     impl Sealed for super::StringType {}