feat(hw): add banked CAM pipeline with grouped read/write noise

- Add cam_core_banked.sv with 8-lane banked CAM core
- Add cam_write_noise.sv and cam_read_noise.sv for grouped noise injection
- Add noise_mask_grouped.sv generating grouped flip masks from 128-bit PRNG
- Add match_engine_pipeline.sv with multi-stage pipelined top-1 selection
- Add popcount_pipeline.sv for pipelined popcount operations
- Refactor test_cam_basic.py with parametrized DUT introspection helpers
- Add Python ref_model match_top1_with_read_noise() for read noise verification
- Update Makefile with separate WRITE_NOISE_* and READ_NOISE_* parameter groups
- Add new testbenches: test_cam_core_banked, test_cam_read_noise,
  test_cam_write_noise, test_match_engine_pipeline, test_ref_model_noise
  
breaking change hint: NUM_ROWS default changed from 512→4096, LANES from 16→8

hw/rtl/noise_mask_grouped.sv

@@ -0,0 +1,37 @@
+`timescale 1ns / 1ps
+`include "cam_params.svh"
+
+module noise_mask_grouped #(
+    parameter int HASH_BITS      = `HASH_BITS,
+    parameter int NOISE_BITS     = 8,
+    parameter int NOISE_RATE_NUM = 1,
+    parameter int NOISE_RATE_DEN = 100
+) (
+    input  logic [127:0]          random_i,
+    output logic [HASH_BITS-1:0]  mask_o
+);
+    localparam int GROUP_BITS       = HASH_BITS / NOISE_BITS;
+    localparam int BIT_INDEX_BITS   = 6;
+    localparam int SAMPLE_BITS      = 8;
+    localparam int GROUP_RAND_BITS  = BIT_INDEX_BITS + SAMPLE_BITS;
+    localparam int SAMPLE_RANGE     = 1 << SAMPLE_BITS;
+    localparam int THRESHOLD        = (NOISE_RATE_NUM * SAMPLE_RANGE) / NOISE_RATE_DEN;
+
+    initial begin
+        if (NOISE_BITS <= 0) $fatal(1, "NOISE_BITS must be > 0");
+        if (HASH_BITS % NOISE_BITS != 0) $fatal(1, "HASH_BITS must be divisible by NOISE_BITS");
+        if (GROUP_BITS != 64) $fatal(1, "GROUP_BITS must be 64 for 6-bit grouped noise");
+        if (NOISE_BITS * GROUP_RAND_BITS > 128) $fatal(1, "NOISE_BITS consumes more than 128 random bits");
+        if (NOISE_RATE_DEN <= 0) $fatal(1, "NOISE_RATE_DEN must be > 0");
+        if (NOISE_RATE_NUM < 0 || NOISE_RATE_NUM > NOISE_RATE_DEN) $fatal(1, "NOISE_RATE_NUM out of range");
+    end
+
+    always_comb begin
+        mask_o = '0;
+        for (int i = 0; i < NOISE_BITS; i++) begin
+            if (random_i[i * GROUP_RAND_BITS + BIT_INDEX_BITS +: SAMPLE_BITS] < THRESHOLD) begin
+                mask_o[i * GROUP_BITS + random_i[i * GROUP_RAND_BITS +: BIT_INDEX_BITS]] = 1'b1;
+            end
+        end
+    end
+endmodule