Fix conversions for Rust 1.89 compatibility

[RAprogramm]

Summary

• add a test-only backtrace preference override, remove the StdError::backtrace implementation, and update tests to avoid mutating RUST_BACKTRACE
• harden integration converters for tonic, redis, config, serde_json, and sqlx to avoid deprecated APIs and unsized metadata
• bump the crate to 0.20.2, refresh README/changelog guidance, and regenerate all trybuild .stderr expectations

Testing

• cargo +nightly fmt --
• cargo +1.90.0 clippy -- -D warnings
• cargo +1.90.0 build --all-targets
• cargo +1.90.0 test --all
• cargo +1.90.0 doc --no-deps
• cargo deny check
• cargo audit

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https://chatgpt.com/codex/tasks/task_e_68d368e90a08832b8f84d95f20f18eae