fix: eddblink retrieval (progress, bandwidth)

[kfsone]

• reduce the amount of data transferred to determine if there is new eddblink data, previously we were downloading each file twice roughly,
• capture the uncompressed file-length during the probe, so we can show the user an accurate progres bar

To test:

• run trade.py import -P eddblink, observe that a progress bar renders during download of listings.csv
• remove one or more data\eddb*.csv file and rerun eddblink import to confirm it sees the files as stale and redownloads the files.