Restrict cache pickle deserialization

[3em0]

Summary

• add a restricted cache unpickler that only allows AD Miner cache model classes and basic containers
• route cache loading in both the main cache class and analyse_cache.py through the restricted loader
• preserve direct execution of analyse_cache.py by adding an import fallback for local script execution

Fixes #238

Verification

• python -m compileall ad_miner/scripts/analyse_cache.py ad_miner/sources/modules/cache_class.py ad_miner/sources/modules/cache_security.py
• malicious pickle PoC is rejected with Unsupported cache object: builtins.eval and does not create the marker file
• legitimate AD Miner Node/Path cache object still loads through the restricted loader