Deregister native FIPS error callback on library cleanup or reset

[cconlon]

This PR cleans up use of the native wolfSSL FIPS callback, resetting it back to null to prevent possible issues where it could be called from native wolfSSL after the Java provider has been garbage collected.

• Call wolfCrypt_SetCb_fips(NULL) before deleting the Java global ref to fully deregister the native callback
• When called with a NULL callback, now properly calls wolfCrypt_SetCb_fips(NULL) instead of only deleting the Java global ref
• Add NULL guard for g_fipsCbIfaceObj in NativeFIPSErrorCallback() before calling GetObjectRefType (undefined behavior on NULL), and return silently on invalid references instead of throwing exceptions from the C callback

[Copilot]

Pull request overview

This PR improves lifecycle management for the wolfCrypt FIPS error callback by explicitly deregistering the native callback and hardening the native-to-Java callback path against invalid/cleared references during cleanup/reset.

Changes:

• Deregister the native wolfCrypt FIPS callback during WolfSSL.cleanup().
• Ensure setFIPSCb(NULL) deregisters the native callback (not just the Java global ref).
• Add guards in NativeFIPSErrorCallback() to avoid JNI UB on NULL/invalid callback references and avoid throwing from within the C callback.

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