Function einsum_with_pool 

pub fn einsum_with_pool<'a>(
    notation: &str,
    operands: Vec<EinsumOperand<'a>>,
    size_dict: Option<&HashMap<char, usize>>,
    pool: Option<&mut BufferPool>,
) -> Result<EinsumOperand<'a>>

Parse and evaluate an einsum expression with optional buffer pool reuse.

Pass Some(&mut pool) to reuse intermediate buffers across calls. Pass None for independent allocation (equivalent to einsum).