refactor(hw/sim): extract common cocotb make infrastructure into shared mk/ directory

- Split monolithic hw/sim/Makefile into modular include files (mk/cocotb-common.mk, mk/rtl-sources.mk)
- Add per-module test Makefiles (cam_core_banked, cam_read_noise, cam_write_noise, match_engine_pipeline, perf, top)
- Add missing simulation tools (yosys, graphviz, xdot) to devenv.nix
- Fix path handling in sweep_noise.py and test modules to be HASH_BITS-aware

hw/sim/tests/modules/cam_read_noise/Makefile

@@ -0,0 +1,15 @@
+SIM_ROOT := $(abspath ../../..)
+RTL_ROOT := $(abspath $(SIM_ROOT)/../rtl)
+include $(SIM_ROOT)/mk/rtl-sources.mk
+
+TOPLEVEL := cam_read_noise
+COCOTB_TEST_MODULES := tests.modules.cam_read_noise.test_cam_read_noise
+VERILOG_SOURCES := $(RTL_READ_NOISE)
+
+HASH_BITS ?= 512
+READ_NOISE_EN ?= 0
+READ_NOISE_RATE_NUM ?= 0
+READ_NOISE_RATE_DEN ?= 100
+READ_NOISE_BITS ?= $(shell echo $$(( $(HASH_BITS) / 64 )))
+
+include $(SIM_ROOT)/mk/cocotb-common.mk

hw/sim/tests/modules/cam_read_noise/test_cam_read_noise.py

@@ -0,0 +1,49 @@
+from __future__ import annotations
+
+import cocotb
+from cocotb.clock import Clock
+from cocotb.triggers import RisingEdge
+
+
+async def reset_read_noise(dut):
+    dut.rst_n.value = 0
+    dut.valid_i.value = 0
+    dut.row_ids_i.value = 0
+    dut.hashes_i.value = 0
+    dut.lane_valid_i.value = 0
+    for _ in range(3):
+        await RisingEdge(dut.clk)
+    dut.rst_n.value = 1
+    for _ in range(2):
+        await RisingEdge(dut.clk)
+
+
+@cocotb.test()
+async def read_noise_disabled_forwards_hashes_after_one_stage(dut):
+    cocotb.start_soon(Clock(dut.clk, 10, unit="ns").start())
+    await reset_read_noise(dut)
+
+    LANES = len(dut.lane_valid_i)
+    ROW_BITS = len(dut.row_ids_i) // LANES
+    HASH_BITS_PER_LANE = len(dut.hashes_i) // LANES
+    all_lanes_valid = (1 << LANES) - 1
+
+    hashes = 0
+    rows = 0
+    for lane in range(LANES):
+        hashes |= (lane + 0x55) << (lane * HASH_BITS_PER_LANE)
+        rows |= lane << (lane * ROW_BITS)
+
+    dut.hashes_i.value = hashes
+    dut.row_ids_i.value = rows
+    dut.lane_valid_i.value = all_lanes_valid
+    dut.valid_i.value = 1
+    await RisingEdge(dut.clk)
+    dut.valid_i.value = 0
+    await RisingEdge(dut.clk)
+    await RisingEdge(dut.clk)
+
+    assert int(dut.valid_o.value) == 1
+    assert int(dut.hashes_noisy_o.value) == hashes
+    assert int(dut.row_ids_o.value) == rows
+    assert int(dut.lane_valid_o.value) == all_lanes_valid