feat(solana): CAR download script

[sistemd]

No description provided.

[claude]

Review of the Solana CAR download script and solana_compare tracing improvements.

Key findings (by priority):

1. Performance — blocking sync I/O in async context: fs_err::exists, fs_err::create_dir_all, and fs_err::metadata are blocking calls on async worker threads. Use tokio::fs equivalents.

2. Panic branch: .expect("invalid range header") should return an error instead of panicking.

3. Durability for resume: flush() doesn't guarantee data persistence to disk. Use sync_all() since the resume logic depends on accurate on-disk file sizes.

4. No integrity verification: Only file size is checked for completeness. A corrupted or truncated download would not be detected.

5. No reqwest timeout: Default client has no connect/read timeout, meaning a stalled connection could hang indefinitely without triggering a retry.

6. Guideline violations: Missing doc comments on CarDownloadError, abbreviated log field names, non-standard duration logging format, and #[from] usage on error variants.

7. DRY: env_filter_or_info is duplicated verbatim across two example files.

[claude]

Follow-up: additional logging guideline findings from docs/code/logging-errors.md.

[leoyvens]

Object storage support will be important