Remove unnecessary safe-buffer dependency (use Node.js built-in Buffer API)

[hdsuperman]

Hi, I noticed that the project depends on safe-buffer. This dependency was mainly needed for very old Node.js versions (<6) that didn’t support the modern Buffer APIs.

Since all actively supported Node.js versions now include Buffer.from and Buffer.alloc natively, the safe-buffer dependency is no longer necessary. Removing it would help reduce install size and dependency tree complexity.

Additionally, safe-buffer can cause issues in modern ESM builds:

• The package relies on require("buffer") internally.
• When bundled as ESM (e.g. with esbuild/rollup/webpack), this leads to runtime errors such as
  Error: Dynamic require of "buffer" is not supported.

Suggested change:

• Replace require('safe-buffer').Buffer with the built-in Buffer global.
• Drop safe-buffer from dependencies.

This should be fully backwards-compatible for all currently supported Node.js versions (>=12, >=14, >=16, etc.).

Thanks!

[mahmoodhamdi]

Fixed in #115. I also opened a PR for the same issue in node-jwa (auth0/node-jwa#57) since both packages share this dependency.