Refactor: Extract duplicated response truncation logic into helper method

[Copilot]

Addresses code review feedback on PR #26 to eliminate duplicated response text truncation logic in the Agent365 exporter's HTTP retry handler.

Changes

• Added helper method: _truncate_text(text: str, max_length: int) -> str as a static method that handles truncation with ellipsis appending
• Deduplicated logging: Replaced two inline truncation expressions (200 and 500 char limits) with calls to the helper method

# Before
f"Response: {resp.text[:200]}{'...' if len(resp.text) > 200 else ''}"
response_text = resp.text[:500] + ("..." if len(resp.text) > 500 else "")

# After  
f"Response: {self._truncate_text(resp.text, 200)}"
response_text = self._truncate_text(resp.text, 500)

This ensures consistent truncation behavior and improves maintainability without changing existing functionality.

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[Copilot]

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