Prepare 4.0.0 release (#1232)

Author: rly

CHANGELOG.md

@@ -1,6 +1,6 @@
 # HDMF Changelog
 
-## [Unreleased]
+## HDMF 4.0.0 (January 22, 2025)
 
 ### Breaking changes
 - The following classes have been deprecated and removed: Array, AbstractSortedArray, SortedArray, LinSpace, Query, RegionSlicer, ListSlicer, H5RegionSlicer, DataRegion, RegionBuilder. The following methods have been deprecated and removed: fmt_docval_args, call_docval_func, get_container_cls, add_child, set_dataio (now refactored as set_data_io). We have also removed all early development for region references. @mavaylon1, @rly [#1998](https://github.com/hdmf-dev/hdmf/pull/1198), [#1212](https://github.com/hdmf-dev/hdmf/pull/1212)