Ch440 review fixes: 93-bit per-bank test coverage + soften M20K claims [READY FOR REVIEW]

Per Codex review of 471c1af:
1. tb_gs_async_fifo QUAD_WIDTH4 variant now runs at the PRODUCTION 93-bit width
   (exercising the odd 23/23/23/24 remainder split) and drives a DISTINCT NONZERO
   pattern into every width bank (seq XOR per-bank constants, bank2 inverted), with
   the scoreboard checking the FULL reconstructed word. A swapped/broken/zeroed
   upper bank now changes the word and trips the scoreboard. Depth-half crossing
   (DEPTH=8) + wrap/full coverage retained. mk() is generate-guarded so the 32-bit
   variants never elaborate the 93-bit selects.
2. Softened gs_async_fifo comments: 'same total M20K' -> EXPECTED-similar, pending
   synthesis (fact -> expectation).

No simulations or Quartus run. Awaiting review before any sim.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

rtl/gif_gs/gs_async_fifo.sv

@@ -31,8 +31,9 @@ module gs_async_fifo #(
     parameter bit QUADRANT_READ = 1'b0,
     // Ch440: two depth banks x FOUR width banks (eight physical RAMs). Like
     // QUADRANT_READ but splits the payload into four width banks instead of two,
-    // halving each preserved read-address register's M20K load AGAIN at the same
-    // total M20K, while KEEPING QUADRANT_READ's 2:1 depth output selector (no
+    // halving each preserved read-address register's M20K load AGAIN (total M20K
+    // is EXPECTED to stay ~the same, pending synthesis), while KEEPING
+    // QUADRANT_READ's 2:1 depth output selector (no
     // new/deeper output mux). Depth, one-cycle read latency, ordering, capacity,
     // and interface behaviour are identical to QUADRANT_READ.
     parameter bit QUAD_WIDTH4_READ = 1'b0
@@ -174,7 +175,8 @@ module gs_async_fifo #(
         if (QUAD_WIDTH4_READ) begin : g_quad_width4_storage
             // Ch440: 2 depth banks x 4 width banks = eight RAMs.  Each read-address
             // register drives only a HALF_DEPTH x ~(WIDTH/4) RAM -> roughly half the
-            // M20K load of QUADRANT_READ's hi/lo banks, at the SAME total M20K.  The
+            // M20K load of QUADRANT_READ's hi/lo banks, at an EXPECTED-similar total
+            // M20K (pending synthesis confirmation).  The
             // depth-half selection stays a 2:1 OUTPUT mux, byte-for-byte the selector
             // QUADRANT_READ already uses -- no new/deeper output mux is introduced.
             localparam int W4B0 = WIDTH/4;