feat: external PLE file loading (#31185)
* model : allow loading external PLE files
Assisted-by: Codex
* convert : add separate PLE exports
Assisted-by: Codex
* tests : fix PLE export test lint
Assisted-by: Codex
* model : make --ple an alias of --shard, allow multiple shard locations
Reuse the multi-shard loading path for external PLE files instead of a
separate option.
* --ple is an alias of --shard: both take a comma separated list and may
be given more than once, and the shards may live anywhere
* metadata comes from the main file; numbered shards are still
auto-discovered and strictly validated
* explicit files outside the discovered set are appended as extra shards,
exempt from split.no and split.count checks
* -isnm/--ignore-shard-num-mismatch loads only the given files, in order,
with no auto-discovery and no split metadata validation
* ple_path, path_ple and llama_model_loader::add_ple_file are removed;
common_model_load() uses llama_model_load_from_splits for two or more
paths
* common/fit.{h,cpp} take the shard path vector, so --fit and the router
memory measurement load every shard
Assisted-by: GPT-6-Astra
* rm -isnm
* make sure to dedup paths
* rm test_convert_ple
* address comments
* allow ple shard to override tensor
---------
Co-authored-by: Xuan Son Nguyen <son@huggingface.co>
