Declare SecKeyOperationType as CFIndex, matching SecKey.h

[LucaCappelletti94]

security-framework-sys declares SecKeyOperationType as u32, while Apple declares it as CF_ENUM(CFIndex, SecKeyOperationType), and CFIndex is a signed long, 8 bytes on every target the crate supports. SecKeyIsAlgorithmSupported takes it by value, so the caller writes a 32-bit value while the callee reads a 64-bit register whose upper half is everybody's guess.

Looking into the current issues, no misbehaviour has been reported, and the high-level crate never calls the function, so the risk is definitely latent and I suppose low priority.

The systest binary catches it when run on macOS 26.6.2 (bad SecKeyOperationType size: rust: 4 (0x4) != c 8 (0x8), with matching lines for alignment and signedness).