Pre-compile HAR schema for validation

Ajv is currently used in httpsnippet for validating the HAR schema passed. Using complete Ajv dependency makes httpsnippet require 'unsafe-eval in the CSP policy, which is a security concern. (https://github.com/ajv-validator/ajv/blob/c3e203c2696e42ec107fe6a5a659fca54b2e4993/docs/security.md#content-security-policy).

As a workaround, since the schema for HAR is known (and already included), it can be pre-compiled into a validation function as part of the build. The Ajv Docs have details on the same.

This would move Ajv from a runtime dependency to a optional developer-dependency (as Ajv-cli) - only needed when har-schema is updated. This would bring a lot more benefits, including performance and bundle size improvements.

This request comes via the Stoplight Elements project, which uses httpsnippet internally. Since httpsnippet doesn't offer a way to pre-compile schemas, this ends up breaking Elements in configurations which limit unsafe-eval via CSP.

src/helpers/har-validator.ts から始め、含まれている HAR スキーマが現在どのように検証されているかを調べてください。Ajv CLI の compile-schemas に関するガイダンスとリポジトリの build 設定を読み、生成された検証コードを配置すべき場所を特定してください。検証に実行時の Ajv や unsafe-eval が不要になり、Ajv がオプションの開発依存関係だけになり、既存の検証テストが通れば完了です。