fix: re-add vendor/nim-ffi submodule to fix C-bindings build

`requires` in the nimble file alone is not sufficient, NBS never calls
`nimble install` or clones URLs from the `requires` block at build time.
The package must be present as a git submodule for NBS to discover and
link it.

Migrating to `nimble install` is a separate task.

.gitmodules

@@ -24,3 +24,7 @@
 [submodule "vendor/libchat"]
 	path = vendor/libchat
 	url = https://github.com/logos-messaging/libchat.git
+[submodule "vendor/nim-ffi"]
+	path = vendor/nim-ffi
+	url = https://github.com/logos-messaging/nim-ffi.git
+	branch = master

logos_chat.nimble

@@ -15,12 +15,10 @@ requires "nim >= 2.2.4",
   "blake2",
   "chronicles",
   "libp2p",
-  "nimchacha20poly1305", # TODO: remove
   "confutils",
   "eth",
   "regex",
   "web3",
-  "https://github.com/jazzz/nim-sds#exports",
   "libchat",
   "waku",
   "ffi"
@@ -79,5 +77,5 @@ task pingpong, "Build the Pingpong example":
   buildBinary name, "examples/", "-d:chronicles_log_level='INFO' -d:chronicles_disabled_topics='waku node' "
 
 task liblogoschat, "Build the Logos-Chat shared library (C bindings)":
-  buildLibrary "logoschat", "library/", 
+  buildLibrary "logoschat", "library/",
     "-d:chronicles_log_level='INFO' -d:chronicles_enabled=on --path:src --path:vendor/nim-ffi"

vendor/nim-ffi

@@ -0,0 +1 @@
+Subproject commit c2c03f1f0f300ec3aab8b733fe97575f452f6133