Python: Bump Python package versions for 1.12.1 release

[Evan Mattson (moonbox3)]

Motivation & Context

Bump root and core to 1.12.1, OpenAI to 1.11.0 for new public prompt-cache options, Foundry to 1.10.3, and Gemini and Foundry Hosting to beta 260722 based on CHANGELOG entries. No beta cohort bump was applied, and core floors remain unchanged under the strict affected-dependency policy because the connectors do not require a new core API.

Description & Review Guide

• What are the major changes?
• What is the impact of these changes?
• What do you want reviewers to focus on?

Related Issue

Fixes #

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and title prefix in sync automatically.

[Copilot]

Pull request overview

This PR prepares the Python monorepo for the python-1.12.1 release by updating package versions, the root meta-package pin, the workspace lockfile, and the Python changelog release section/links.

Changes:

• Bump agent-framework and agent-framework-core to 1.12.1, and update the root meta-package dependency pin to agent-framework-core[all]==1.12.1.
• Bump connector package versions: agent-framework-openai to 1.11.0, agent-framework-foundry to 1.10.3, and agent-framework-gemini / agent-framework-foundry-hosting to 1.0.0b260722.
• Add the 1.12.1 release section to python/CHANGELOG.md and update footer compare links; update python/uv.lock to reflect the new workspace versions.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
python/uv.lock	Updates workspace-locked package versions to match the release bumps.
python/pyproject.toml	Bumps root agent-framework to 1.12.1 and pins agent-framework-core[all]==1.12.1.
python/packages/core/pyproject.toml	Bumps agent-framework-core version to 1.12.1.
python/packages/openai/pyproject.toml	Bumps agent-framework-openai version to 1.11.0.
python/packages/foundry/pyproject.toml	Bumps agent-framework-foundry version to 1.10.3.
python/packages/gemini/pyproject.toml	Bumps agent-framework-gemini beta version date stamp to b260722.
python/packages/foundry_hosting/pyproject.toml	Bumps agent-framework-foundry-hosting beta version date stamp to b260722.
python/CHANGELOG.md	Adds 1.12.1 release notes and updates compare links for the new release tag.

[github-actions]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
TOTAL	45259	4451	90%

report-only-changed-files is enabled. No files were changed during this commit :)

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
9368	33 💤	0 ❌	0 🔥	1m 59s ⏱️