Function calculate_safe_concurrency 

pub fn calculate_safe_concurrency(
    available_mb: u64,
    cpu_count: usize,
    ram_per_task_mb: u64,
    max_concurrency: usize,
) -> usize

Calculates the safe concurrency ceiling for heavy embedding workloads.

Canonical formula: permits = min(cpus, available_memory_mb / ram_per_task_mb) * 0.5

The result is clamped between 1 and max_concurrency.