Format panic payloads before logging

[leynos]

Summary

• format panic payloads before logging to improve clarity
• update test helpers to format panic payloads
• cover non-string panic payloads in tests

Testing

• make fmt
• make lint
• make test

closes #218

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https://chatgpt.com/codex/tasks/task_e_68a2cd7acb7883228480c0ec8ea02932

Summary by Sourcery

Format panic payloads consistently before logging by converting string payloads to owned strings and using Debug formatting for non-string panics

Enhancements:

• Update connection task logging to unwrap &str and String panics as owned strings and format all other panic payloads with Debug instead of a placeholder
• Apply the same panic payload formatting logic in the Wireframe testing helper

Tests:

• Add a spawn_connection_task test to assert that non-string panic payloads are logged with their Debug representation