Disable pretty-print when saving tokenizer.json files

### Feature request

As the vocabulary of newer models, like Llama 3 or Gemma, increases in size, so does the size of the tokenizer, which includes the vocabulary as JSON (and merges for BPE tokenizers). Pretty-printing these files for serialization introduces a significant overhead as whitespace around the vocabulary and/or merges is added to the file.

This issue is even worse after the new BPE serialization update, which replaces merges like `"s1 s2"` with `["s1", "s2"]`, which is now formatted to be on separate lines:


From quick testing, not pretty-printing the tokenizer.json reduces the file size from 17MB to 7MB.

Understandably, pretty-printing the file can help with debugging, but for those cases, it's probably better that the default is not formatted (and have a flag for outputting with formatting).

cc @ArthurZucker
(PS: I can move this to `huggingface/tokenizers` if it is more applicable there.

### Motivation

To reduce the file sizes (and bandwidth) of downloading, serializing, and uploading these files. In particular, this will greatly benefit Transformers.js users, where bandwidth is important.

### Your contribution

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