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/model/test_ref_model_noise.py

@@ -0,0 +1,70 @@
+from __future__ import annotations
+
+from model.ref_model import (
+    generate_grouped_flip_mask,
+    match_top1_with_read_noise,
+    xnor_popcount_score,
+)
+
+
+def test_grouped_flip_mask_full_rate_one_bit_per_64_bit_group():
+    random_value = 0
+    for group in range(8):
+        bit_idx = group + 1
+        sample = 0
+        random_value |= bit_idx << (group * 14)
+        random_value |= sample << (group * 14 + 6)
+
+    mask = generate_grouped_flip_mask(
+        random_value=random_value,
+        hash_bits=512,
+        noise_bits=8,
+        rate_num=1,
+        rate_den=1,
+    )
+
+    expected = 0
+    for group in range(8):
+        expected |= 1 << (group * 64 + group + 1)
+
+    assert mask == expected
+    assert mask.bit_count() == 8
+
+
+def test_grouped_flip_mask_zero_rate_no_flips():
+    mask = generate_grouped_flip_mask(
+        random_value=(1 << 128) - 1,
+        hash_bits=512,
+        noise_bits=8,
+        rate_num=0,
+        rate_den=100,
+    )
+    assert mask == 0
+
+
+def test_score_is_bit_match_popcount_not_hamming_distance():
+    query = 0b1010
+    stored = 0b1000
+    assert xnor_popcount_score(query, stored, width=4) == 3
+
+
+def test_read_noise_model_is_reproducible_after_reset_seed():
+    rows = [0, (1 << 512) - 1, 0x1234, 0x5678, 0x9ABC, 0xDEF0, 0x1357, 0x2468]
+    query = rows[2]
+    kwargs = dict(
+        query=query,
+        rows=rows,
+        width=512,
+        lanes=8,
+        noise_bits=8,
+        rate_num=1,
+        rate_den=100,
+        seed=0x6A09_E667_F3BC_C909,
+    )
+
+    first = match_top1_with_read_noise(**kwargs)
+    second = match_top1_with_read_noise(**kwargs)
+
+    assert first.top1_index == second.top1_index
+    assert first.top1_score == second.top1_score
+    assert first.scores.tolist() == second.scores.tolist()