refactor: skip hparams the loader stores but never reads

[PABannier]

The three hparams loaders (sam3_load_hparams, sam2_load_hparams, edgetam_load_extra_hparams) read 16 header fields into sam3_hparams that nothing reads again. The code hard-codes the behaviour those flags describe.

Loader	Fields skipped
SAM3	ddec_ffn_dim, n_presence_tokens, n_geom_queries, n_amb_experts
SAM2	use_high_res_features, use_obj_ptrs_in_encoder, directly_add_no_mem_embed, non_overlap_masks_for_mem_enc, binarize_mask_from_pts, multimask_output_for_tracking, multimask_min_pt_num, multimask_max_pt_num, iou_prediction_use_sigmoid, use_mask_input_as_output
EdgeTAM	mem_attn_ca_q_size, mem_attn_ca_k_size

These fields are removed from the struct. Each loader gets a skip(n) lambda (fin.seekg(4 * n, cur)), with the skipped field names in a trailing comment so the on-disk layout stays readable. The .ggml format doesn't change; converters still write every field.

Verification: a parity tool loads models through both SAM2 paths (SAM2.1 Hiera and EdgeTAM extra hparams), then compares encode, PVS point + box, and a 3-frame visual track byte for byte with origin/main:

PARITY OK   edgetam_f16 gpu0
PARITY OK   edgetam_f16 gpu1
PARITY OK   sam2.1_hiera_tiny_q8_0 gpu0
PARITY OK   sam2.1_hiera_tiny_q8_0 gpu1

The SAM3 loader only has a compile check, because no full SAM3 checkpoint is available locally. Its change is three rd → skip swaps in the same positions.

git diff --shortstat: 1 file changed, 11 insertions(+), 32 deletions(-).

Part of an over-engineering cleanup series.

🤖 Generated with Claude Code

https://claude.ai/code/session_01M2qLmQ9ag49hT61V6i9qAq