Fix duplicate hybrid search result subscription

[arnabnandy7]

Description

Fixes an intermittent IndexOutOfBoundsException when executing cross-partition hybrid search queries using ORDER BY RANK RRF(...).

The coalesced component-query results were consumed by two reactive branches. Because the result Mono was cold, each branch independently re-executed the cross-partition query pipeline and could receive a differently sized result list. The ranks calculated from one result set could then be applied to another, causing the exception.

This change caches the coalesced result Mono, ensuring rank calculation and RRF score calculation operate on the same materialized results.

Fixes #49823.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which has an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

The azure-cosmos module was successfully compiled for both the Java baseline and module-path build. No new automated test was added because reproducing the original failure requires nondeterministic timing differences between duplicate subscriptions to a live, cross-partition query. Existing hybrid-search integration tests continue to cover RRF query execution.

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[Copilot]

Pull request overview

This PR fixes an intermittent IndexOutOfBoundsException in cross-partition hybrid search queries (ORDER BY RANK RRF(...)) by ensuring the coalesced component-query results are materialized once and shared across downstream reactive branches, preventing mismatched rank/score computations caused by duplicate subscriptions.

Changes:

• Cached the coalesced-and-sorted hybrid search result Mono to prevent duplicate re-execution and inconsistent result sizing across reactive branches.
• Added a CHANGELOG entry documenting the bug fix and linking to the tracked issue.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/query/HybridSearchDocumentQueryExecutionContext.java	Adds .cache() to the coalesced-and-sorted results Mono so rank and RRF computations consume the same materialized result set.
sdk/cosmos/azure-cosmos/CHANGELOG.md	Documents the hybrid search cross-partition IndexOutOfBoundsException fix and references Issue #49823.