Search is slow to respond

STR
Try a search for something new
Watch the DM console
Notice how browser pauses while DM is working to do something - not sure what,

Output of console is e.g.
```
dweb-transports:httptools Fetch of https://dweb.me/arc/archive.org/advancedsearch?output=json&q=byron%20bay&rows=30&page=1&sort[]=-downloads&and[]=&save=yes&fl=identifier%2Ctitle%2Ccollection%2Cmediatype%2Cdownloads%2Ccreator%2Cnum_reviews%2Cpublicdate%2Citem_count%2Cloans__status__status completed +4s
dweb-mirror:MirrorFS Already cached existing file with matching sha1 /Volumes/Transcend/archiveorg/THEBLUESROOM64911JULY2018MIDGEMARSDENTRIBUTE/__ia_thumb.jpg +34s
dweb-mirror:MirrorFS Already cached existing file with matching sha1 /Volumes/Transcend/archiveorg/THEBLUESROOM6484JULY2018HOUROFBLUESPOWERWITHDARCYPERRY/__ia_thumb.jpg +5ms
dweb-mirror:MirrorFS Already cached existing file with matching sha1 /Volumes/Transcend/archiveorg/THEBLUESROOM65018JULY2018BELLYFULLABLUESWITHFATTMAX/__ia_thumb.jpg +693ms
dweb-mirror:MirrorFS Already cached existing file with matching sha1 /Volumes/Transcend/archiveorg/eits2012-07-27.aud/__ia_thumb.jpg +30ms
dweb-mirror:MirrorFS Already cached existing file with matching sha1 /Volumes/Transcend/archiveorg/jbt2003-07-20.flac/__ia_thumb.jpg +385ms
dweb-mirror:MirrorFS Already cached existing file with matching sha1 /Volumes/Transcend/archiveorg/JimmyNooneJrWithDaviesRhythmic5605SweetLorraine/__ia_thumb.jpg +740ms
dweb-mirror:MirrorFS Already cached existing file with matching sha1 /Volumes/Transcend/archiveorg/PoorMansWhiskey2016-03-04/__ia_thumb.jpg +1s
dweb-transports:httptools p_httpfetch: https://dweb.me/info '' +9s
dweb-transports:httptools Fetch of https://dweb.me/info completed +3s
GET /arc/archive.org/advancedsearch?output=json&q=byron%20bay&rows=30&page=1&sort[]=-downloads&and[]=&save=yes&fl=identifier%2Ctitle%2Ccollection%2Cmediatype%2Cdownloads%2Ccreator%2Cnum_reviews%2Cpublicdate%2Citem_count%2Cloans__status__status - 200 25159 29693.270 ms
```
Which looks like its checking/fetching thumbnails before returning

Reproduce a search for “byron bay” and inspect the DM console and the /arc/archive.org/advancedsearch request shown in the report. Trace why thumbnail or cache work occurs before the response completes; done means the search no longer pauses while that unrelated work is performed, with the reported request timing improved.

Written by the indexing model from the issue text.