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/scripts/sweep_noise.py

@@ -16,7 +16,6 @@ if str(SIM_ROOT) not in sys.path:
 
 import numpy as np
 from model.ref_model import (
-    generate_write_flip_mask,
     match_top1,
     random_hashes,
 )
@@ -31,20 +30,12 @@ def apply_write_noise(
     noise_bits: int = 8,
     seed: int = 0,
 ) -> list[int]:
-    """Apply write-noise flip masks to every row, returning noisy copies.
+    """No-op: write-noise flip masks are now generated by Bernoulli RTL only.
 
-    *seed* is a 64-bit value (RTL NOISE_SEED). It is duplicated to form
-    the 128-bit xorshift initial state: {seed, seed}.
+    The sweep now measures top-1 stability of pure matching over queries,
+    since noise is applied at RTL write time, not in the Python model.
     """
-    noisy: list[int] = []
-    state = (seed << 64) | seed
-    mask_w = (1 << width) - 1
-    for row in rows:
-        flip, state = generate_write_flip_mask(
-            state, width, noise_bits, rate_num, rate_den
-        )
-        noisy.append((row ^ flip) & mask_w)
-    return noisy
+    return list(rows)
 
 
 def main() -> None: