[qwen3.5] fix DTensor TP vision position caches

[pianpwk]

Stack from ghstack (oldest at bottom):

• [spmd_types] qwen3.5 enablement #3895
• -> [qwen3.5] fix DTensor TP vision position caches #3899

Main TP was failing with FLA_TILELANG=0 MODULE=qwen3_5 CONFIG=qwen35_debugmodel NGPU=2 ./run_train.sh --parallelism.tensor_parallel_degree 2 --parallelism.data_parallel_shard_degree 1 --debug.seed 42 --debug.deterministic --training.steps 1

[rank0]:[rank0]:   File "/data/users/pianpwk/full_spmd_types_torchtitan/tt4_spmd_types/torchtitan/torchtitan/models/qwen3_5/vision_encoder.py", line 91, in _compute_learned_pos_embeds
[rank0]:[rank0]:     pos_hw = F.interpolate(
[rank0]:[rank0]:              ^^^^^^^^^^^^^^
[rank0]:[rank0]:   File "/data/users/pianpwk/full_spmd_types_torchtitan/pytorch/torch/nn/functional.py", line 5273, in interpolate
[rank0]:[rank0]:     )._upsample_linear_vec(input, output_size, align_corners, scale_factors)
[rank0]:[rank0]:       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[rank0]:[rank0]:   File "/data/users/pianpwk/full_spmd_types_torchtitan/pytorch/torch/_decomp/decompositions.py", line 4507, in _upsample_linear_vec
[rank0]:[rank0]:     return _upsample_linear(input, osize, align_corners, scales)
[rank0]:[rank0]:            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[rank0]:[rank0]:   File "/data/users/pianpwk/full_spmd_types_torchtitan/pytorch/torch/_decomp/decompositions.py", line 91, in inner
[rank0]:[rank0]:     r = f(*tree_map(increase_prec, args), **tree_map(increase_prec, kwargs))
[rank0]:[rank0]:         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[rank0]:[rank0]:   File "/data/users/pianpwk/full_spmd_types_torchtitan/pytorch/torch/_decomp/decompositions.py", line 4627, in _upsample_linear
[rank0]:[rank0]:     v = aten._unsafe_index(input, idx)
[rank0]:[rank0]:         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[rank0]:[rank0]:   File "/data/users/pianpwk/full_spmd_types_torchtitan/pytorch/torch/_ops.py", line 1350, in __call__
[rank0]:[rank0]:     return self._op(*args, **kwargs)
[rank0]:[rank0]:            ^^^^^^^^^^^^^^^^^^^^^^^^^
[rank0]:[rank0]: RuntimeError: aten._unsafe_index.Tensor got mixed torch.Tensor and DTensor, need to convert all torch.Tensor to DTensor before calling distributed operators!

• DTensor decomposition goes to unsafe_index which creates local plain tensors - fixes by local-mapping interpolate
• upcoming spmd_types PR would parallelize inv_freq, get ahead of this by also wrapping positions as DTensors - previously that portion was done in plain tensor

[tianyu-l]

pls make sure numerics doesn't change