feat!: 700% faster deepCopyObject, refactor deep merging and deep copying, type improvements (#7272)

**BREAKING:**
- The `deepMerge` exported from payload now handles more complex data and
is slower. The old, simple deepMerge is now exported as `deepMergeSimple`
- `combineMerge` is no longer exported. You can use
`deepMergeWithCombinedArrays` instead
- The behavior of the exported `deepCopyObject` and `isPlainObject` may
be different and more reliable, as the underlying algorithm has changed

test/localization/int.spec.ts

@@ -286,7 +286,7 @@ describe('Localization', () => {
         const post = await payload.create({
           collection: localizedSortSlug,
           data: {
-            date: new Date(),
+            date: new Date().toISOString(),
             title: `EN ${i}`,
           },
           locale: englishLocale,
@@ -296,7 +296,7 @@ describe('Localization', () => {
           id: post.id,
           collection: localizedSortSlug,
           data: {
-            date: new Date(),
+            date: new Date().toISOString(),
             title: `ES ${i}`,
           },
           locale: spanishLocale,