chore: update 9 stale fuzz targets for cachekit-core 0.1.1 API

[27Bslash6]

Problem

9 of 14 fuzz targets in rust/fuzz/ fail to compile against cachekit-core 0.1.1. The API has evolved (e.g., encrypt_aes_gcm renamed to encrypt_with_keys, StorageEnvelope field changes) but the fuzz targets were never updated.

Broken targets

Target	Error
encryption_roundtrip	no method named encrypt_aes_gcm
encryption_nonce_reuse	no method named encrypt_aes_gcm
encryption_truncated_ciphertext	no method named decrypt_aes_gcm
encryption_aad_injection	no method named encrypt_aes_gcm
encryption_large_payload	no method named encrypt_aes_gcm
integration_layered_security	no method named encrypt_aes_gcm + trait bounds
byte_storage_corrupted_envelope	StorageEnvelope field access changes
byte_storage_integer_overflow	StorageEnvelope field access changes
byte_storage_empty_data	StorageEnvelope field access changes
byte_storage_checksum_collision	StorageEnvelope field access changes

Working targets (4)

• byte_storage_compress
• byte_storage_decompress
• byte_storage_format_injection
• encryption_key_derivation

Additional fix needed

rust/fuzz/Cargo.toml previously depended on the non-existent package cachekit-storage. Fixed in PR #113 to depend on cachekit-core directly (the fuzz targets use cachekit-core's internal module paths).

Scope

Update all 9 broken fuzz targets to match cachekit-core 0.1.1's current API. No new targets needed.