fix: Add Extra Check for Reformatted Root Node in GetNode (backport #1007)

[mergify]

Problem Description

When the root node is reformatted due to pruning, its nodeKey changes from (version, 1) to (version, 0). As a result:

1.	This version becomes invisible during a root search.
2.	If a node in the next version references the reformatted node, it becomes inaccessible.

Proposed Solution

Add an extra check in the GetNode function to handle reformatted root nodes. This ensures that:

•	Reformatted nodes with nodeKey (version, 0) remain accessible.
•	References to these nodes from subsequent versions are correctly resolved.

Summary by CodeRabbit

• New Features

  • Introduced a new test to validate the behavior of the MutableTree after version deletions.
  • Added new APIs: DeleteVersionsFrom(int64) and GetLatestVersion.

• Bug Fixes

  • Enhanced the GetNode method to improve retrieval logic for nodes, ensuring better handling of cases with nil buffers and legacy nodes.

• Documentation

  • Updated the changelog to reflect recent improvements and fixes, including a new section for bug fixes and detailed descriptions of changes.

---

This is an automatic backport of pull request #1007 done by [Mergify](https://mergify.com).

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