Remove Codecov bundle analysis integration (#255)

This PR removes the Codecov bundle analysis integration from the
project.

## Summary
Removes Codecov rollup plugin configuration and related CI/CD steps that
were used for bundle analysis tracking.

## Key changes
- Removed `@codecov/rollup-plugin` dependency from `package.json`
- Removed codecov plugin configuration from `tsdown.config.ts`
- Simplified GitHub Actions workflow by removing:
  - Build step with `CODECOV_TOKEN` environment variable
  - Codecov upload action step
  - Replaced with a simple `pnpm run build` command

## Details
The bundle analysis feature was previously integrated via the Codecov
rollup plugin, which would analyze and upload bundle metrics during the
build process. This integration has been completely removed, simplifying
both the build configuration and CI/CD pipeline while reducing external
dependencies.

https://claude.ai/code/session_01VmhNxzgxxEyHCkW1F6RQ66

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: bartveneman

.github/workflows/test.yml

@@ -22,15 +22,7 @@ jobs:
           cache: pnpm
       - run: pnpm install --frozen-lockfile --ignore-scripts
       - run: pnpm run test-coverage
-      - name: Build with bundle analysis
-        run: pnpm run build
-        env:
-          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
-      - name: Upload coverage reports to Codecov
-        uses: codecov/codecov-action@57e3a136b779b570ffcdbf80b3bdc90e7fab3de2 # v6
-        with:
-          token: ${{ secrets.CODECOV_TOKEN }}
-          slug: projectwallace/css-parser
+      - run: pnpm run build
 
   check-ts:
     name: Check types

package.json

@@ -86,7 +86,6 @@
 		"precommit": "pnpm run test -- --run; pnpm run lint; pnpm run check"
 	},
 	"devDependencies": {
-		"@codecov/rollup-plugin": "^2.0.1",
 		"@projectwallace/preset-oxlint": "^0.0.10",
 		"@types/node": "^24.10.1",
 		"@vitest/coverage-v8": "^4.1.5",