chore(layers): drop unused infer_swatten_* helpers

The three `infer_swatten_*` state-dict introspection helpers in
`compressai/layers/attn/inference.py` were intended for MambaIC /
MambaVC `from_state_dict`, but neither model is part of this PR. No
code in this PR (stf.py, swin.py, tests) calls them. Removing per
"don't add infrastructure for hypothetical future PRs" — the helpers
can be reintroduced alongside the first model that actually uses them.

Author: Yiozolm

compressai/layers/attn/__init__.py

@@ -1,8 +1,3 @@
-from .inference import (
-    infer_swatten_attention_dim,
-    infer_swatten_head_dim,
-    infer_swatten_window_size,
-)
 from .swin import (
     WMSA,
     ConvTransBlock,
@@ -30,9 +25,6 @@
     "WinResidualUnit",
     "WindowAttention",
     "build_window_attention_mask",
-    "infer_swatten_attention_dim",
-    "infer_swatten_head_dim",
-    "infer_swatten_window_size",
     "pad_to_window_multiple",
     "window_partition",
     "window_reverse",