refactor(hw/sim): reorganize CAM top-level tests into per-noise-config suites

Split the monolithic test_cam_basic.py into separate test suites
organized by noise configuration (no_noise, write_noise, read_noise),
with shared utilities extracted to tests/top/utils.py.

- Remove test_cam_basic.py; add no_noise/, write_noise/, read_noise/
  test suites with Makefiles that set noise parameters statically
- Extract helpers (reset_dut, write_rows, query_once, collect_topk,
  etc.) into tests/top/utils.py
- Update hw/sim/Makefile with per-config test targets and a
  test-top-all meta-target
- Update scripts/run_cam_correctness.py to build per-directory
  instead of centrally, removing inline parameter overrides
- Add __init__.py for result_serializer and topk_tracker module tests
- Expand docstrings in test_ref_model_noise.py with architectural
  context and test rationale

hw/sim/tests/top/no_noise/Makefile

@@ -0,0 +1,13 @@
+SIM_ROOT := $(abspath ../../..)
+RTL_ROOT := $(abspath $(SIM_ROOT)/../rtl)
+include $(SIM_ROOT)/mk/rtl-sources.mk
+
+TOPLEVEL := cam_top
+COCOTB_TEST_MODULES := tests.top.no_noise.test_no_noise
+VERILOG_SOURCES := $(RTL_CAM_TOP)
+
+# 禁用所有噪声模块
+WRITE_NOISE_EN := 0
+READ_NOISE_EN := 0
+
+include $(SIM_ROOT)/mk/cocotb-common.mk