Python: Include InvokeAzureAgent input.arguments in agent text

[Shivani . (Shivani767)]

Motivation & Context

InvokeAzureAgentExecutor._build_input_text() evaluated input.arguments into evaluated_args and then never used that dict. Actions that supply only input.arguments (as in the customer_support sample) therefore invoked the agent with an empty string.

Fixes #7902

Description & Review Guide

• What are the major changes?

  • Format evaluated input.arguments as key: value lines (same shape as multi-value Workflow.Inputs fallback).
  • Include that text in the agent input, alone or combined with explicit messages / fallback input.
  • Add regression tests for arguments-only, arguments+messages, and expression-valued arguments.

• What is the impact of these changes?

  • Argument-only InvokeAzureAgent actions now pass structured values to agent.run().
  • Existing messages-only and fallback-input behavior is unchanged when no arguments are present.

• What do you want reviewers to focus on?

  • Whether folding arguments into text is the right Python parity approach vs. a Foundry structured_inputs channel (.NET uses the latter; Python run() has no equivalent parameter).

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

Fixes #7902 by preserving evaluated InvokeAzureAgent arguments in agent input text.

Changes:

• Formats arguments as key: value lines.
• Combines arguments with explicit or fallback message text.
• Adds regression coverage for argument-only, combined, and expression-based inputs.

Reviewed changes

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

File	Description
python/packages/declarative/agent_framework_declarative/_workflows/_executors_agents.py	Includes evaluated arguments in agent input text.
python/packages/declarative/tests/test_graph_coverage.py	Adds regression tests for argument handling.

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