fix: skip unsupported keys when loading JWK set in IdTokenVerifier

[arib06]

skip keys without a supported algorithm (RS256/ES256) or without a kid when loading a JWK set, so a single unsupported key no longer aborts the whole set with a NullPointerException from ImmutableMap and fails verification of validly signed tokens from that issuer.

PublicKeyLoader.buildPublicKey returns null for an unsupported algorithm and kid is optional per RFC 7517, but the loop that builds the key cache catches only the key-factory exceptions, not the ImmutableMap.Builder.put(null) NPE, so one unusable key in an otherwise valid key set defeats the existing skip-bad-key handling.

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