Raise ruff line-length to 100 and extend the local pre-commit format pipeline (def-signature magic-comma normalization, short multi-line assert collapse, kwarg '=' spacing, blank-line-after-short-import removal, adjacent string-literal / f-string+plain merge, redundant-pass pruning). Every transform re-checks the file AST and is dropped if it would differ; the whole-repo reformat is verified AST-identical per file and idempotent.
Preserves the source tokenizer's eos_token in tokenizer_config.json after merged saves so runtimes such as vLLM read the correct stop token. Centralized inside the patched tokenizer save_pretrained so all save paths (merged_16bit, GGUF, torchao, push_to_hub) benefit, with filename_prefix support.
Fixes#5386
