Quadratic-time key_ops duplicate check lets a sub-1 MB JWKS body pin a CPU core for ~15 s

`jwkFields.CheckConsistency` detected duplicate `key_ops` entries with a pairwise nested loop, making validation cost grow with the **square** of the entry count. Because the check runs on every JWK and JWKS unmarshal, a modestly sized but hostile JWKS document could occupy a CPU core for many seconds.