fix: set spia mem_mb to 32G and threads to 32 (#154)

`spia` uses a lot of memory, and we have observed above 20G of memory
usage. To be safe, we reserve a bit more. The cores we set to a power of
2, as that will often align with the number of cores available on
machines.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Chores**
* Adjusted resource allocation for the enrichment workflow to use fewer
threads and set a specific memory limit.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: dlaehnemann

workflow/rules/enrichment.smk

@@ -22,7 +22,9 @@ rule spia:
         enrichment_env
     log:
         "logs/tables/pathways/{model}.spia-pathways.log",
-    threads: 38
+    threads: 32
+    resources:
+        mem_mb=32000,
     script:
         "../scripts/spia.R"