* mtmd : allow multiple modalities at the same time
* refactor mtmd tokenizer
* fix compile
* ok, missing SinusoidsPositionEmbedding
* first working version
* fix style
* more strict validate of n_embd
* refactor if..else to switch
* fix regression
* add test for 3B
* update docs
* fix tokenizing with add_special
* add more tests
* fix test case "huge"
* rm redundant code
* set_position_mrope_1d rm n_tokens
