implemented benchmarks

.github/workflows/codspeed.yml

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+name: codspeed-benchmarks
+
+on:
+    push:
+        branches:
+            - 'main' # or "main"
+    pull_request:
+    workflow_dispatch:
+
+jobs:
+    benchmarks:
+        runs-on: ubuntu-latest
+        steps:
+            - uses: actions/checkout@v4
+            - name: Use Node.js 20
+              uses: actions/setup-node@v4
+              with:
+                  node-version: 20.11.1
+                  # More info: https://docs.github.com/en/actions/publishing-packages/publishing-nodejs-packages#publishing-packages-to-the-npm-registry
+                  registry-url: 'https://registry.npmjs.org'
+            - name: Use node_modules cache
+              uses: actions/cache@v4
+              with:
+                  path: node_modules
+                  key: yarn-node-20-lock-${{ hashFiles('yarn.lock') }}
+                  restore-keys: |
+                      yarn-node-20-lock-
+            - run: yarn install --frozen-lockfile
+            - name: Run benchmarks
+              uses: CodSpeedHQ/action@v3
+              with:
+                  token: ${{ secrets.CODSPEED_TOKEN }}
+                  run: 'yarn bench'

benchmarks/bench.ts

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+import { Bench } from 'tinybench'
+import { withCodSpeed } from '@codspeed/tinybench-plugin'
+
+import { twMerge } from '../src/index'
+
+import testData from './perf-test-data.json'
+
+const bench = withCodSpeed(new Bench())
+
+bench.add('twMerge (simple)', () => {
+    twMerge('flex mx-10 px-10', 'mr-5 pr-5')
+})
+
+bench.add('twMerge (heavy)', () => {
+    twMerge(
+        'font-medium text-sm leading-16',
+        'group/button relative isolate items-center justify-center overflow-hidden rounded-md outline-none transition [-webkit-app-region:no-drag] focus-visible:ring focus-visible:ring-primary',
+        'inline-flex',
+        'bg-primary-50 ring ring-primary-200',
+        'text-primary dark:text-primary-900 hover:bg-primary-100',
+        false,
+        'font-medium text-sm leading-16 gap-4 px-6 py-4',
+        null,
+        'p-0 size-24',
+        null,
+    )
+})
+bench.add('twMerge (collection)', () => {
+    for (let i = 0; i < testData.length; ++i) {
+        type Item = (typeof testData)[number][number]
+        twMerge(...(testData[i] as Exclude<Item, true>[]))
+    }
+})
+;(async () => {
+    await bench.run()
+    console.table(bench.table())
+})()