Fix Skani OOM: dynamic mem_gb scaled to bin sizes

Replace fixed 16 GB with 32 + 4*size(bins) so light samples stay cheap
and heavy samples (many/large bins) get enough headroom for the GTDB r226
marker hash table load.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: tpshea2

wdl/tasks/MAG/Skani.wdl

@@ -33,6 +33,7 @@ task Skani {
     }
 
     Int disk_size = 20 + ceil(3.0 * size(skani_db_tgz, "GB")) + ceil(2.0 * size(bins, "GB"))
+    Int mem_size  = 32 + ceil(4.0 * size(bins, "GB"))
 
     command <<<
         set -euxo pipefail
@@ -69,7 +70,7 @@ task Skani {
 
     RuntimeAttr default_attr = object {
         cpu_cores:         24,
-        mem_gb:            16,
+        mem_gb:            mem_size,
         disk_gb:           disk_size,
         boot_disk_gb:      25,
         preemptible_tries: 2,