Design a position limit checker that determines whether a new order would cause
the net position to exceed a configurable limit.

Module name: pos_limit
Parameters:
  - WIDTH = 32       // Data width

Ports:
  - input  signed [WIDTH-1:0] current_pos  // Current net position
  - input  [WIDTH-1:0]        order_qty    // Proposed order quantity
  - input                     is_buy       // 1 = buy, 0 = sell
  - input  [WIDTH-1:0]        limit        // Maximum allowed |position|
  - output                    allow        // Order is within limits
  - output                    reject       // Order would exceed limits

Functional specification:
  - Computes prospective position: buy adds qty, sell subtracts qty
  - Rejects if |new_position| > limit
  - allow and reject are complementary (exactly one is high)
  - Purely combinational (no clock)
