CopyObject takes the reader and decodes it with jsontext, accepting
repeated names and invalid UTF-8 as encoding/json did. Keys are written
with the bytes they were read with instead of being re-encoded. Member
gets Skip, which reads past a value without keeping it, and npm's
RewriteStream skips dropped versions and duplicates with it.
conda-forge noarch repodata.json (195 MB): filtering 0.89 to 0.62 s and
379 to 77 MB allocated, the timestamp index 0.84 to 0.61 s. The next
packument (32 MB): RewriteStream 69 to 34 ms and 38 to 3.5 MB.
