chore: bump nim-ffi to v0.1.5-rc.2

Picks up the foreign-host (Go) concurrency fixes from nim-ffi #83:
the caller-thread GC allocation in ffiNewReq, GC-rooting of myLib under
refc, and the NimMain first-time-init race. Without them, sds-go-bindings
crashes under concurrent wrap/unwrap and manager creation.

sds-go-bindings' full suite incl. the concurrent stress tests and -race
pass against rc.2 (refc).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

nimble.lock

@@ -209,8 +209,8 @@
       }
     },
     "ffi": {
-      "version": "#v0.1.5-rc.1",
-      "vcsRevision": "e86b136e793adc9617e3c85ff4e8abe256a80100",
+      "version": "#v0.1.5-rc.2",
+      "vcsRevision": "0a6bf6c49ff8d956899c2a3bb3a2b3ab8ed5281f",
       "url": "https://github.com/logos-messaging/nim-ffi",
       "downloadMethod": "git",
       "dependencies": [
@@ -219,7 +219,7 @@
         "taskpools"
       ],
       "checksums": {
-        "sha1": "301ae3a3a6889a1641a102a2c74798d1d82e6efb"
+        "sha1": "eea561ccabe2f5fff6a586fbbf83d4e4dc41a7fb"
       }
     }
   },

sds.nimble

@@ -16,7 +16,7 @@ requires "stew"
 requires "stint"
 requires "metrics"
 requires "results"
-requires "https://github.com/logos-messaging/nim-ffi#v0.1.5-rc.1"
+requires "https://github.com/logos-messaging/nim-ffi#v0.1.5-rc.2"
 
 proc buildLibrary(
     outLibNameAndExt: string,