chore(deps): upgrade vitest from v3 to v4 (#642)

## Summary
- Upgrade vitest from ^3.2.4 to ^4.0.17
- Upgrade @vitest/coverage-v8 from ^3.2.4 to ^4.0.17
- Add `--reporter=dot` to vitest run commands for cleaner output
- Add conditional vitest@3 downgrade for Node 16/18 in CI (vitest@4
requires Node 20+)

## Test plan
- [x] Local tests pass with vitest@4 on Node 20+
- [x] Coverage report generates correctly
- [x] Benchmarks run successfully
- [x] CI passes for Node 20, 22, 24 (vitest@4)
- [x] CI passes for Node 18 (vitest@3 downgrade)
- [x] CI passes for Node 16 (vitest@3 downgrade)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Chores**
  * Updated vitest and coverage tooling to v4.0.17.
  * Enhanced test output formatting with dot reporter.
  * Improved CI workflows for Node.js version compatibility.
  * Refined build configuration structure.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: fengmk2

.github/workflows/nodejs-16.yml

@@ -20,6 +20,8 @@ jobs:
         with:
           node-version: 16
       - run: npm install
+      - name: Downgrade vitest for Node 16
+        run: npm install vitest@3 @vitest/coverage-v8@3 --save-dev --ignore-scripts
       - run: npm run ci:node16
       - run: npm run prepublishOnly
       - run: node -v

.github/workflows/nodejs.yml

@@ -77,6 +77,10 @@ jobs:
       - name: Install dependencies
         run: pnpm install --frozen-lockfile
 
+      - name: Downgrade vitest for Node 18
+        if: matrix.node == '18'
+        run: pnpm add vitest@3 @vitest/coverage-v8@3 --save-dev --ignore-scripts
+
       - name: Run tests
         run: pnpm run ci
 

package.json

@@ -61,13 +61,13 @@
     "test-tsc:cjs": "cd test/fixtures/ts && rm -rf node_modules && npm link ../../.. && npm run build",
     "test-tsc:cjs:es2021": "cd test/fixtures/ts-cjs-es2021 && rm -rf node_modules && npm link ../../.. && npm run build",
     "test-tsc:esm": "cd test/fixtures/ts-esm && rm -rf node_modules && npm link ../../.. && npm run build",
-    "test": "npm run lint -- --fix && vitest run",
+    "test": "npm run lint -- --fix && vitest run --reporter=dot",
     "bench": "vitest bench",
-    "test-keepalive": "cross-env TEST_KEEPALIVE_COUNT=50 vitest run --test-timeout 180000 keep-alive-header.test.ts",
+    "test-keepalive": "cross-env TEST_KEEPALIVE_COUNT=50 vitest run --reporter=dot --test-timeout 180000 keep-alive-header.test.ts",
     "test-node16": "node examples/httpclient.cjs && node examples/search_github.cjs && node examples/timing.cjs",
-    "cov": "vitest run --coverage",
+    "cov": "vitest run --reporter=dot --coverage",
     "ci": "npm run cov && npm run prepublishOnly && npm pack && attw --pack",
-    "ci:node16": "cross-env NODE_OPTIONS=\"--require ./test/patch-for-node16-18.cjs\" vitest run && npm run prepublishOnly && npm pack && attw --pack",
+    "ci:node16": "cross-env NODE_OPTIONS=\"--require ./test/patch-for-node16-18.cjs\" vitest run --reporter=dot && npm run prepublishOnly && npm pack && attw --pack",
     "clean": "rm -rf dist && tsc -b --clean",
     "prepublishOnly": "npm run build",
     "prepare": "husky"
@@ -95,7 +95,7 @@
     "@types/tar-stream": "^2.2.3",
     "@typescript/native-preview": "7.0.0-dev.20260114.1",
     "@ungap/structured-clone": "^1.3.0",
-    "@vitest/coverage-v8": "^3.2.4",
+    "@vitest/coverage-v8": "^4.0.17",
     "busboy": "^1.6.0",
     "cross-env": "^10.1.0",
     "husky": "^9.1.7",
@@ -111,7 +111,7 @@
     "tshy": "^3.1.0",
     "tshy-after": "^1.4.1",
     "typescript": "^5.9.3",
-    "vitest": "^3.2.4"
+    "vitest": "^4.0.17"
   },
   "lint-staged": {
     "*": [