Memory exhaustion via oversized decode_base64 bytes setting

Uncontrolled resource allocation in Suricata before 7.0.9 allows local users to starve memory through an untrusted decode_base64 rule. The decode_base64 parser accepts a bytes value as a 32-bit unsigned integer and sizes the per-thread decoded-data buffer from the largest configured value, permitting an allocation approaching 4 GiB for each thread. Loading an attacker-supplied signature containing an oversized value is required, and the resulting resource starvation can interrupt the detection engine without disclosing or altering data.