.Net & Python: Add tool definitions to agent invoke span

[TaoChenOSU]

Motivation and Context

The current GenAI Semantic Conventions have changed since the last time we modified the agent_invoke span.

Previous PRs: #12940, #12928, #12834

Description

The following changes were made:

1. gen_ai.agent.invocation_input -> gen_ai.input.messages
2. gen_ai.agent.invocation_output -> gen_ai.output.messages
3. Add gen_ai.tool.definitions

.Net:

Python:

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[moonbox3]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
utils/telemetry/agent_diagnostics
decorators.py	120	11	90%	163, 195, 199, 203, 243–248, 253
gen_ai_attributes.py	8	0	100%
TOTAL	27293	4770	82%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3747	22 💤	0 ❌	0 🔥	1m 41s ⏱️