fix: ensure CSP nonces are Base64 encoded

[paulbalandan]

Description
Per CSP specification, CSP nonces are base64 encoded values appended to nonce-. In the framework's implementation, we're using bin2hex which results in hexadecimal encoded values instead.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[michalsn]

Nice catch.