style(phi4mm): replace ambiguous Unicode in comments for clean lint

Replace the multiplication-sign U+00D7 and arrow U+2192 in NaViT mask
comments with ASCII (x, ->) to clear ruff RUF003 warnings, so lintrunner
runs warning-free.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Signed-off-by: Justin Chu <11205048+justinchuby@users.noreply.github.com>

Author: justinchuby

src/mobius/models/phi.py

@@ -495,7 +495,7 @@ def forward(
         pos_w = op.Div(op.Mul(c, p_const), nb_w_div)  # (N, 1, P)
         # pos_id(r,c) = pos_h * P + pos_w → (N, P, P)
         pos_id = op.Add(op.Mul(pos_h, p_const), pos_w)
-        # Valid patches are the top-left nb_h × nb_w block; others → id 0.
+        # Valid patches are the top-left nb_h x nb_w block; others -> id 0.
         valid = op.And(op.Less(r, nb_h), op.Less(c, nb_w))  # (N, P, P)
         zero = op.Constant(value_int=0)
         pos_id = op.Where(valid, pos_id, zero)
@@ -959,9 +959,9 @@ def forward(
         # ── Optional mask crop: drop padded sub-crop rows/cols ────────
         # HF (modeling_phi4mm.py:376-382) uses image_attention_mask to crop
         # the assembled grid to its useful height/width before adding the
-        # row separators.  The mask is at the pre-AvgPool resolution (H×H);
+        # row separators.  The mask is at the pre-AvgPool resolution (HxH);
         # HF samples it stride-2 (``[..., 0::2, 0::2]``) so each value maps
-        # to one post-AvgPool position (Hp×Hp per crop).
+        # to one post-AvgPool position (HpxHp per crop).
         if image_attention_mask is not None:
             # Sub-crop masks: crops 1..B_ → (h*w, H, H)
             sub_mask = op.Slice(