fix(rspack): fix issue with optimization options in rspack config (#31337)

## Current Behavior
rspack.config.ts options related to optimizations are removed if the
mode is not "production". This makes the compile fail for all
non-production builds.

## Expected Behavior
If mode isn't set to "production" configuration related to optimization
should be passed through.

## Related Issue(s)
Fixes #31268 #30292

packages/rspack/src/plugins/utils/apply-base-config.ts

@@ -147,10 +147,10 @@ function applyNxIndependentConfig(
     ...(config.ignoreWarnings ?? []),
   ];
 
-  config.optimization = !isProd
+  config.optimization = {
-    ? undefined
-    : {
     ...(config.optimization ?? {}),
+    ...(isProd
+      ? {
           sideEffects: true,
           minimize:
             typeof options.optimization === 'object'
@@ -182,6 +182,8 @@ function applyNxIndependentConfig(
           runtimeChunk: isDevServer
             ? config.optimization?.runtimeChunk ?? undefined
             : false,
+        }
+      : {}),
   };
 
   config.stats = {