feat(hw/rtl): add xorshift PRNG modules and refactor cam_noisy FSM

- Add random32, random64 and random128 xorshift PRNG modules
- Refactor cam_noisy FSM: split state register, next-state logic, and datapath into distinct blocks
- Rename state_q/state_d to curr_state/next_state for clarity
- Add MASK_GROUPS localparam and fix type casting in noise generation
- Update .gitignore to exclude docs/superpowers

hw/rtl/random/random64.sv

@@ -0,0 +1,28 @@
+`timescale 1ns / 1ps
+
+module random64 (
+    input  logic        clk,
+    input  logic        rst_n,
+    input  logic        enable,
+    input  logic [63:0] seed,
+    output logic [63:0] out
+);
+
+    function automatic logic [63:0] xorshift64(input logic [63:0] x);
+        logic [63:0] s;
+        s = x;
+        s ^= s << 13;
+        s ^= s >> 7;
+        s ^= s << 17;
+        return s;
+    endfunction
+
+    always_ff @(posedge clk or negedge rst_n) begin
+        if (!rst_n) begin
+            out <= seed;
+        end else if (enable) begin
+            out <= xorshift64(out);
+        end
+    end
+
+endmodule