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

docs/experiments.md

@@ -31,7 +31,7 @@
 - `hw/rtl/core/popcount_pipeline.sv`
 - `hw/rtl/noise/cam_write_noise.sv`
 - `hw/rtl/noise/cam_read_noise.sv`
-- `hw/rtl/noise/noise_mask_grouped.sv`
+- `hw/rtl/noise/noise_mask_bernoulli.sv`（Phase 2 后 read noise 改为 pass-through，该模块仅用于 write noise mask 生成）
 - `hw/rtl/cam_params.svh`
 - `hw/sim/model/ref_model.py`
 - `hw/sim/sweep_noise.py`
@@ -129,7 +129,7 @@
 
 - 写入/读取：`hw/rtl/core/cam_core_banked.sv`、`hw/sim/tests/test_cam_core_banked.py`
 - 匹配与 popcount：`hw/rtl/core/match_engine_pipeline.sv`、`hw/rtl/core/popcount_pipeline.sv`
-- 噪声模块：`hw/rtl/noise/cam_write_noise.sv`、`hw/rtl/noise/cam_read_noise.sv`
+- 噪声模块：`hw/rtl/noise/cam_write_noise.sv`、`hw/rtl/noise/cam_read_noise.sv`（Phase 2 后 read noise 改为 pass-through，实际翻转仅由 write noise 模块产生）
 - 参考模型：`hw/sim/model/ref_model.py`
 - 集成测试：`hw/sim/tests/test_cam_basic.py`