feat: use parallel version of bzip2 to decompress gisaid snapshot

I don't know if it's any faster, but why now.

The results are correct in my local testing.

Locally, it does use multiple threads, but not too many. We might be bound by download speed rather then decompression though.

Related: #242

Dockerfile

@@ -34,7 +34,8 @@ FROM nextstrain/base:branch-python-base
 RUN apt-get update && apt-get install -y --no-install-recommends \
         python3-netifaces \
         time\
-        xz-utils
+        xz-utils \
+        lbzip2
 
 # Install Python deps
 RUN python3 -m pip install pipenv

bin/fetch-from-gisaid

@@ -7,4 +7,4 @@ set -euo pipefail
 curl "$GISAID_API_ENDPOINT" \
     --user "$GISAID_USERNAME_AND_PASSWORD" \
     --fail --silent --show-error --location-trusted --http1.1 \
-    | bunzip2
+    | lbzip2 -d