feat: add per-generator NIST health tests and dead-ring monitor, onod3000 output test (FPGA v4)

fpga/rtl/entropy_generator.v

@@ -16,6 +16,7 @@ module entropy_generator #(
     input  wire [7:0] ring_select,  // ring exposed on the characterization outputs
     output reg        out_bit,      // processed output, held for `temporal` clocks
     output wire       spatial_bit,  // XOR of all rings, one per clock
+    output wire [RINGS-1:0] ring_samples,  // synchronized enhanced outputs, for health tests
     output reg        ring_enhanced,
     output reg        ring_tap,
     output wire       ring_raw_tap  // unsynchronized, for frequency counting
@@ -62,7 +63,8 @@ module entropy_generator #(
         level4 <= ^level3;
     end
 
-    assign spatial_bit = level4;
+    assign spatial_bit  = level4;
+    assign ring_samples = sample_sync;
 
     // Temporal XOR over `temporal` consecutive spatial bits.
     reg [3:0] phase       = 4'd0;