[evaluation] backport 1.16.6 release notes; bump version to 1.16.7

[slister1001]

Backport of the 1.16.6 release metadata to main after the hotfix release shipped to PyPI on 2026-04-27.

Changes

• Set 1.16.6 CHANGELOG date to 2026-04-27 (matches PyPI release date)
• Add [fix] emit evaluation token usage in genai evaluation event #46502 token usage bullet to the 1.16.6 section (this PR's fix shipped in the hotfix but the bullet was added to the CHANGELOG only on the hotfix branch)
• Add empty 1.16.7 (Unreleased) section above 1.16.6
• Bump _version.py to 1.16.7

Hotfix branch reference

Released from hotfix/azure-ai-evaluation/1.16.6 containing:

• [evaluation] Fix multi-turn red team attacks broken by PyRIT 0.11 #46444 — multi-turn red team / PyRIT 0.11 fix
• Fix SDL false-pass by normalizing string context in attack objectives #46445 — SDL string-context normalization
• [fix] emit evaluation token usage in genai evaluation event #46502 — emit evaluation token usage in genai evaluation event

No source code changes — those are already in main.

[Copilot]

Pull request overview

Backports the azure-ai-evaluation 1.16.6 release metadata from the hotfix branch to main and advances main to the next development version (1.16.7).

Changes:

• Add 1.16.7 (Unreleased) section and move 1.16.6 to a dated release (2026-04-27).
• Backfill the missing 1.16.6 changelog bullet for token-usage telemetry.
• Bump the package version constant to 1.16.7.

Reviewed changes

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

File	Description
sdk/evaluation/azure-ai-evaluation/azure/ai/evaluation/_version.py	Bumps VERSION to 1.16.7 to match the new top-of-changelog unreleased version.
sdk/evaluation/azure-ai-evaluation/CHANGELOG.md	Adds 1.16.7 unreleased header, dates 1.16.6 to the PyPI ship date, and includes the missing token-usage fix entry.