Use WebCrypto instead for performance & bundle size improvements

[memcorrupt]

See #296 for original issue.

---

This package uses jsSHA as a dependency, which adds 21.4 kB to the bundle size (ESM minified). This is ~77.4% of this module's bundle size.

The WebCrypto API (including SubtleCrypto) is widely supported in browsers (while using HTTPS), and provides native implementations of crypto functions. Additionally, it supports all the currently supported algorithms in hmac-digest.js except SHA-224; however, only SHA-1, SHA-256, and SHA-512 are actually specified in the TOTP RFC.

Additionally, because the library's dependencies are currently bundled, jsSHA may be unnecessarily bundled in a final project multiple times if dependent projects contain files or dependencies that require jsSHA.

Since Web Crypto API is asynchronous only, this improvement could either be implemented as a breaking change, or with seperate asynchronous generate/validate methods that include the Web Crypto implementation.