fix: RSA from JWK sometimes returns empty Instance

[NReib]

#589 addresses specification difference between JWK (or JWA) and ASN1 integers.

See https://datatracker.ietf.org/doc/html/rfc7518#section-6.3.1.1 for the n parameter these kinds of null bytes are stripped and need to be added again.

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[gemini-code-assist]

Code Review

This pull request updates the createPemFromModulusAndExponent method in src/JWK.php to ensure correct ASN1 encoding by prepending a null byte to the modulus and exponent if their first byte is 128 or greater. Feedback was provided regarding styling inconsistencies, such as the use of tabs instead of spaces and missing spaces after control keywords, to maintain consistency with the rest of the codebase.

[gemini-code-assist]

This new block of code has a few styling issues that are inconsistent with the rest of the file:

• An unnecessary blank line has been added.
• Indentation is done with tabs instead of spaces.
• There is no space after the if keyword.

I'd suggest cleaning this up for consistency.

        // Correct encoding for ASN1, as ints are represented as unsigned in jwk
        // but signed in ASN1. Prepending null byte makes it unsigned.
        if (\strlen($mod) > 0 && \ord($mod[0]) >= 128) {
            $mod = \chr(0) . $mod;
        }
        if (\strlen($exp) > 0 && \ord($exp[0]) >= 128) {
            $exp = \chr(0) . $exp;
        }