Fix CDC reset domain bug (P0), strengthen testbenches with 31 structural assertions

Split cdc_adc_to_processing reset_n into src_reset_n/dst_reset_n so source
and destination clock domains use correctly-synchronized resets. Previously
cdc_chirp_counter's destination-side sync chain (100MHz) was reset by
sys_reset_120m_n (120MHz domain), causing 30 CDC critical warnings.

RTL changes:
- cdc_modules.v: split reset port, source logic uses src_reset_n,
  destination sync chains + output logic use dst_reset_n
- radar_system_top.v: cdc_chirp_counter gets proper per-domain resets
- ddc_400m.v: CDC_FIR_i/q use reset_n_400m (src) and reset_n (dst)
- formal/fv_cdc_adc.v: updated wrapper for new port interface

Build 7 fixes (previously untouched):
- radar_transmitter.v: SPI level-shifter assigns, STM32 GPIO CDC sync
- latency_buffer_2159.v: BRAM read registration
- constraints: ft601 IOB -quiet fix
- tb_latency_buffer.v: updated for BRAM changes

Testbench hardening (tb_cdc_modules.v, +31 new assertions):
- A5-A7: split-domain reset tests (staggered deassertion, independent
  dst reset while src active — catches the P0 bug class)
- A8: port connectivity (no X/Z on outputs)
- B7: cdc_single_bit port connectivity
- C6: cdc_handshake reset recovery + port connectivity

Full regression: 13/13 test suites pass (257 total assertions).

9_Firmware/9_2_FPGA/ddc_400m.v

@@ -544,10 +544,11 @@ wire [17:0] fir_d_in_i, fir_d_in_q;
 cdc_adc_to_processing #(
     .WIDTH(18),
     .STAGES(3)
-)CDC_FIR_i(
-    .src_clk(clk_400m),
-    .dst_clk(clk_100m),
-    .reset_n(reset_n),
+)CDC_FIR_i(
+    .src_clk(clk_400m),
+    .dst_clk(clk_100m),
+    .src_reset_n(reset_n_400m),
+    .dst_reset_n(reset_n),
     .src_data(cic_i_out),
     .src_valid(cic_valid_i),
     .dst_data(fir_d_in_i),
@@ -557,10 +558,11 @@ cdc_adc_to_processing #(
 cdc_adc_to_processing #(
     .WIDTH(18),
     .STAGES(3)
-)CDC_FIR_q(
-    .src_clk(clk_400m),
-    .dst_clk(clk_100m),
-    .reset_n(reset_n),
+)CDC_FIR_q(
+    .src_clk(clk_400m),
+    .dst_clk(clk_100m),
+    .src_reset_n(reset_n_400m),
+    .dst_reset_n(reset_n),
     .src_data(cic_q_out),
     .src_valid(cic_valid_q),
     .dst_data(fir_d_in_q),