Code coverage tooling is outdated

The library was running the command `npm run report-coverage` to provide test coverage information. However, the command is causing the CI to fail due to the error:

```
==> Uploading reports
(node:1970) [DEP0040] DeprecationWarning: The `punycode` module is deprecated. Please use a userland alternative instead.
(Use `node --trace-deprecation ...` to show where the warning was created)
/home/runner/work/node-httptransfer/node-httptransfer/node_modules/codecov/lib/codecov.js:212
} else if (result.split('\n').length !== 2) {
^

TypeError: result.split is not a function
at /home/runner/work/node-httptransfer/node-httptransfer/node_modules/codecov/lib/codecov.js:212:25
at /home/runner/work/node-httptransfer/node-httptransfer/node_modules/teeny-request/build/src/index.js:217:17
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
```

Research into `codecov` reveals that it has been deprecated for several years. The script was removed from the CI to unblock development, so the coverage tooling should be updated if coverage statistics are still desired.

まず、npm run report-coverage スクリプトと、以前それを呼び出していた CI 設定を調べます。非推奨の codecov パッケージがどのようにアップロード失敗を引き起こしているかを確認し、coverage が引き続き必要な場合は、サポートされている coverage レポート方法を特定します。非推奨のツールを使わずに coverage ワークフローが正常に実行されれば完了です。

索引モデルが issue の本文から書いたものです。