fix(era-downloader): improve retry logic and error handling in download_to_file

[forkfury]

Fix

Fixes retry logic and error handling in download_to_file.

The previous range-based retry (1..3) was unclear, and errors weren't handled for non-Era1 files.

Partially downloaded files weren't cleaned up on failure.

Changes

• Replace range-based retry with explicit attempt counter (MAX_DOWNLOAD_ATTEMPTS)
• Clean up partially downloaded files before retries
• Propagate errors correctly for both Era1 and Era file types
• Remove failed downloads and invalid checksum files automatically