test: migrate buffer encoding tests to node:test

[raashish1601]

Refs: #47707

Migrate two small legacy script-style parallel tests to node:test:

• test-buffer-badhex.js
• test-bad-unicode.js

The assertions and behavior are unchanged; the test bodies are wrapped in named test() calls.

Validation:

• node --test test/parallel/test-buffer-badhex.js test/parallel/test-bad-unicode.js
• node -c test/parallel/test-buffer-badhex.js
• node -c test/parallel/test-bad-unicode.js
• node tools/eslint/node_modules/eslint/bin/eslint.js test/parallel/test-buffer-badhex.js test/parallel/test-bad-unicode.js

I could not run the project tools/test.py harness in this checkout because there is no built node.exe present.

[lpinca]

Sorry but I think there is no added value here

[avivkeller]

As stated above, this PR, along with the others you’ve opened, adds little meaningful value to the project. In previous interactions, you’ve also responded hostilely toward maintainers when your low-effort contributions were criticized or not merged. Given that pattern, I’m not interested in spending further time reviewing similarly low-quality submissions.

I've left an identical comment and closed your other pull requests.