make cloneCandidate and cloneVariant faster

```
  cloneCandidate - src/candidate.bench.ts > Candidate cloning
    1.72x faster than cloneCandidate (spread)
    74.03x faster than structuredClone
```

Author: RobinMalfait

packages/tailwindcss/src/candidate.bench.ts

@@ -1,6 +1,6 @@
 import { Scanner } from '@tailwindcss/oxide'
 import { bench, describe } from 'vitest'
-import { cloneCandidate, parseCandidate } from './candidate'
+import { cloneCandidate, parseCandidate, type Candidate, type Variant } from './candidate'
 import { buildDesignSystem } from './design-system'
 import { Theme } from './theme'
 
@@ -37,4 +37,58 @@ describe('Candidate cloning', async () => {
       cloneCandidate(candidate)
     }
   })
+
+  bench('cloneCandidate (spread)', () => {
+    for (let candidate of parsedCanddiates) {
+      cloneCandidateSpread(candidate)
+    }
+  })
 })
+
+function cloneCandidateSpread(candidate: Candidate): Candidate {
+  switch (candidate.kind) {
+    case 'arbitrary':
+      return {
+        ...candidate,
+        modifier: candidate.modifier ? { ...candidate.modifier } : null,
+        variants: candidate.variants.map(cloneVariantSpread),
+      }
+
+    case 'static':
+      return { ...candidate, variants: candidate.variants.map(cloneVariantSpread) }
+
+    case 'functional':
+      return {
+        ...candidate,
+        value: candidate.value ? { ...candidate.value } : null,
+        modifier: candidate.modifier ? { ...candidate.modifier } : null,
+        variants: candidate.variants.map(cloneVariantSpread),
+      }
+
+    default:
+      candidate satisfies never
+      throw new Error('Unknown candidate kind')
+  }
+}
+
+function cloneVariantSpread(variant: Variant): Variant {
+  switch (variant.kind) {
+    case 'arbitrary':
+    case 'static':
+      return { ...variant }
+
+    case 'functional':
+      return { ...variant, modifier: variant.modifier ? { ...variant.modifier } : null }
+
+    case 'compound':
+      return {
+        ...variant,
+        variant: cloneVariantSpread(variant.variant),
+        modifier: variant.modifier ? { ...variant.modifier } : null,
+      }
+
+    default:
+      variant satisfies never
+      throw new Error('Unknown variant kind')
+  }
+}

packages/tailwindcss/src/candidate.ts

@@ -219,20 +219,49 @@ export function cloneCandidate(candidate: Candidate): Candidate {
   switch (candidate.kind) {
     case 'arbitrary':
       return {
-        ...candidate,
+        kind: candidate.kind,
+        property: candidate.property,
+        value: candidate.value,
+        modifier: candidate.modifier
+          ? { kind: candidate.modifier.kind, value: candidate.modifier.value }
+          : null,
         variants: candidate.variants.map(cloneVariant),
-        modifier: candidate.modifier ? { ...candidate.modifier } : null,
+        important: candidate.important,
+        raw: candidate.raw,
       }
 
     case 'static':
-      return { ...candidate, variants: candidate.variants.map(cloneVariant) }
+      return {
+        kind: candidate.kind,
+        root: candidate.root,
+        variants: candidate.variants.map(cloneVariant),
+        important: candidate.important,
+        raw: candidate.raw,
+      }
 
     case 'functional':
       return {
-        ...candidate,
+        kind: candidate.kind,
+        root: candidate.root,
+        value: candidate.value
+          ? candidate.value.kind === 'arbitrary'
+            ? {
+                kind: candidate.value.kind,
+                dataType: candidate.value.dataType,
+                value: candidate.value.value,
+              }
+            : {
+                kind: candidate.value.kind,
+                value: candidate.value.value,
+                fraction: candidate.value.fraction,
+              }
+          : null,
+        modifier: candidate.modifier
+          ? { kind: candidate.modifier.kind, value: candidate.modifier.value }
+          : null,
         variants: candidate.variants.map(cloneVariant),
-        value: candidate.value ? { ...candidate.value } : null,
-        modifier: candidate.modifier ? { ...candidate.modifier } : null,
+        important: candidate.important,
+        raw: candidate.raw,
       }
 
     default:
@@ -244,23 +273,29 @@ export function cloneCandidate(candidate: Candidate): Candidate {
 export function cloneVariant(variant: Variant): Variant {
   switch (variant.kind) {
     case 'arbitrary':
-      return { ...variant }
+      return { kind: variant.kind, selector: variant.selector, relative: variant.relative }
 
     case 'static':
-      return { ...variant }
+      return { kind: variant.kind, root: variant.root }
 
     case 'functional':
       return {
-        ...variant,
-        value: variant.value ? { ...variant.value } : null,
-        modifier: variant.modifier ? { ...variant.modifier } : null,
+        kind: variant.kind,
+        root: variant.root,
+        value: variant.value ? { kind: variant.value.kind, value: variant.value.value } : null,
+        modifier: variant.modifier
+          ? { kind: variant.modifier.kind, value: variant.modifier.value }
+          : null,
       }
 
     case 'compound':
       return {
-        ...variant,
+        kind: variant.kind,
+        root: variant.root,
         variant: cloneVariant(variant.variant),
-        modifier: variant.modifier ? { ...variant.modifier } : null,
+        modifier: variant.modifier
+          ? { kind: variant.modifier.kind, value: variant.modifier.value }
+          : null,
       }
 
     default: