[v17] MB-27666: Nested Fields

[CascadingRadium]

• Adds a NestedDocument interface which extends the Document interface, allowing users to visit any sub-documents that may be nested within the parent document.
• Adds a new NewIndexInternalID method to create an IndexInternalID and also extends the API to enable getting the integer value of the IndexInternalID from it.
• Extends the IndexReader interface to support the Ancestors method, which allows the user to fetch the ancestry chain of any document ID given. If the document does not have any ancestors (it is a root document), an ancestry chain containing only the input document is returned.

[Copilot]

Pull Request Overview

This PR introduces support for nested document structures by adding new interfaces and methods for handling hierarchical relationships between documents. The changes enable segments to expose ancestor and descendant document relationships while maintaining backward compatibility with flat segments.

Key changes:

• Added NestedReader interface with Ancestors method for retrieving parent documents
• Introduced NestedDocument interface for documents containing other documents
• Added utility methods for IndexInternalID conversion and manipulation

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
index.go	Adds NestedReader interface, IndexInternalID utility methods, and imports for binary encoding
document.go	Introduces NestedDocument interface for hierarchical document structures

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

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