Add Offset method to Decoder for caching support

The Offset() method returns the current database offset position,
enabling custom unmarshalers to implement caching based on data
location. This addresses performance needs in applications that
load databases with duplicate data structures.

Author: oschwald

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changes
 
+## 2.0.0-beta.5
+
+- Added `Offset()` method to `Decoder` to get the current database offset. This
+  enables custom unmarshalers to implement caching for improved performance when
+  loading databases with duplicate data structures.
+
 ## 2.0.0-beta.4 - 2025-07-05
 
 - **BREAKING CHANGE**: Removed experimental `deserializer` interface and

internal/decoder/decoder.go

@@ -351,6 +351,12 @@ func (d *Decoder) PeekKind() (Kind, error) {
 	return kindNum, nil
 }
 
+// Offset returns the current offset position in the database.
+// This can be used by custom unmarshalers for caching purposes.
+func (d *Decoder) Offset() uint {
+	return d.offset
+}
+
 func (d *Decoder) reset(offset uint) {
 	d.offset = offset
 	d.hasNextOffset = false