Function compute_tail_block_size 

pub fn compute_tail_block_size(head_block_size: usize, ir_len: usize) -> usize

Computes the optimal tail block size for a two-stage convolver using García’s formula (AES 2002).

For a given head block size N and impulse response length T, the optimal tail block size B minimizes the total computational cost of the double-FDL convolution scheme.