Draft: fix: Backoff on io.UnexpectedEOF
Example below for the kind of hammering this fixes.
E0111 14:37:31.516126 1817971 fetcher.go:292] https://ct2025-a.trustasia.com/log2025a: GetRawEntries() failed: failed to read response body: unexpected EOF
E0111 14:37:31.534967 1817971 fetcher.go:292] https://ct2025-a.trustasia.com/log2025a: GetRawEntries() failed: failed to read response body: unexpected EOF
Closes #13.