[CommCoreModule] capture primitive parameter by value

Summary:
Fixes regression introduced in D8887.

This is a solution for [ENG-4926](https://linear.app/comm/issue/ENG-4926/client-backup-upload-issue).

When the code gets to run, the outer function `generateRandomString` may have already returned. This means that `size` might have been destroyed, and there is an undefined reference. That's why this function generates `backupID` with length 0 and as an effect causes `Argon2` to throw `salt too short`.

On dev everything worked, everything happens only on prod when code is more optimized.

I also added casting to the correct type.

Test Plan: Test upload protocol in `Release mode`.

Reviewers: michal, bartek, marcin, tomek

Reviewed By: bartek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D9197

native/cpp/CommonCpp/NativeModules/CommCoreModule.cpp

@@ -930,13 +930,13 @@ jsi::Value CommCoreModule::computeBackupKey(
 
 jsi::Value CommCoreModule::generateRandomString(jsi::Runtime &rt, double size) {
   return createPromiseAsJSIValue(
-      rt,
-      [this, &size](jsi::Runtime &innerRt, std::shared_ptr<Promise> promise) {
-        taskType job = [this, &innerRt, &size, promise]() {
+      rt, [=](jsi::Runtime &innerRt, std::shared_ptr<Promise> promise) {
+        taskType job = [=, &innerRt]() {
           std::string error;
           std::string randomString;
           try {
-            randomString = crypto::Tools::generateRandomString(size);
+            randomString =
+                crypto::Tools::generateRandomString(static_cast<size_t>(size));
           } catch (const std::exception &e) {
             error = "Failed to generate random string for size " +
                 std::to_string(size) + ": " + e.what();