Python: Add observability unit tests to improve coverage

[giles17]

Motivation and Context

Addresses #3356 - improving unit test coverage for the core observability module.

Description

Adds unit tests for observability module. Coverage: 72% to 86%.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? No

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
TOTAL	16171	2323	85%

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

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3517	234 💤	0 ❌	0 🔥	1m 6s ⏱️

[Copilot]

Pull request overview

This pull request adds comprehensive unit tests for the observability module to improve test coverage from 72% to 86%, addressing issue #3356. The new tests cover a wide range of observability functionality including OTel attributes, metric views, instrumentation decorators, span creation, exception handling, and various utility functions.

Changes:

• Added 1,169 lines of new test code covering observability features
• Tests include coverage for agent instrumentation, chat client telemetry, workflow spans, and configuration
• Tests for both enabled and disabled instrumentation scenarios