refactor(cam): remove read noise from noise architecture (Phase 2)

- Make cam_read_noise a pass-through module, removing all noise injection logic
- Switch write noise to use noise_mask_bernoulli instead of noise_mask_grouped
- Add state machine to cam_write_noise for mask generation timing
- Remove noise_mask_grouped.sv (no longer needed)
- Remove read noise parameters from cam_noisy and cam_top
- Update simulation and benchmark code to reflect read noise removal
- Sync documentation to reflect Phase 2 architecture

hw/sim/tests/perf/test_cam_perf.py

@@ -243,7 +243,6 @@ async def cam_perf_benchmark(dut):
     hash_bits = dut_hash_bits(dut)
     lanes = dut_lanes(dut)
     write_noise_en = _get_param(dut, "WRITE_NOISE_EN", 1)
-    read_noise_en = _get_param(dut, "READ_NOISE_EN", 0)
 
     # ── Deterministic query ─────────────────────────────────────────────
     query_hash = 0xAA55_AA55_AA55_AA55_AA55_AA55_AA55_AA55
@@ -271,7 +270,7 @@ async def cam_perf_benchmark(dut):
     )
 
     # ── Correctness assertions (conditional on noise state) ─────────────
-    if not write_noise_en and not read_noise_en:
+    if not write_noise_en:
         # Without noise: stored hash at row 0 == query_hash → exact match.
         assert top1_index == 0, (
             f"Noise disabled: expected top1_index=0 (exact match), got "
@@ -282,7 +281,7 @@ async def cam_perf_benchmark(dut):
             f"{top1_score}"
         )
     else:
-        # With noise: write/read flip masks may corrupt stored values, so
+        # With noise: write flip masks may corrupt stored values, so
         # we cannot reliably assert the exact match.  Instead, confirm a
         # valid non-zero score was produced (the match engine ran).
         assert top1_score > 0, (
@@ -290,10 +289,10 @@ async def cam_perf_benchmark(dut):
             "Match engine returned invalid result."
         )
         dut._log.info(
-            "Noise enabled (WRITE_NOISE_EN=%s, READ_NOISE_EN=%s) — "
+            "Noise enabled (WRITE_NOISE_EN=%s) — "
             "skipping exact top1_index/top1_score assertion. "
             "top1_index=%d top1_score=%d",
-            write_noise_en, read_noise_en, top1_index, top1_score,
+            write_noise_en, top1_index, top1_score,
         )
 
     # ── Machine-readable performance marker ─────────────────────────────