Keep credentials out of app-server logs (#39993)

## Why

App-server logs can be persisted or included in submitted diagnostics, so credentials used by model providers, authentication refreshes, and attestation requests must not appear in diagnostic output.

## What changed

- Add `RedactedString`, which preserves serialization and string access while replacing debug output with `<redacted>`.
- Use it for model-provider bearer tokens, header and query values, authentication command arguments, and attestation tokens.
- Avoid logging JSON-RPC error payloads and parser or authentication errors that may echo credentials; retain safe context such as error codes and categories.

## Testing

- Add an app-server regression test that exercises provider credentials, refreshed authentication tokens, and attestation tokens, then verifies none appear in persisted SQLite or submitted diagnostic logs.

GitOrigin-RevId: 8c50408adf94d93847658b1320682cf3b637d2cc

codex-rs/core/Cargo.toml

@@ -146,6 +146,7 @@ codex-home = { workspace = true }
 codex-otel = { workspace = true }
 codex-test-binary-support = { workspace = true }
 codex-utils-cargo-bin = { workspace = true }
+codex-utils-redacted-string = { workspace = true }
 codex-web-search-extension = { workspace = true }
 core_test_support = { workspace = true }
 ctor = { workspace = true }