fix: model cannot be loaded with custom quantiles

[AzulGarza]

passing different quantiles than DEFAULT_QUANTILES in src.timesfm.timesfm_base (eg. quantiles=[0.3, 0.4]) throws the following error:

which makes sense if the decoder was hardcoded to output that size of quantiles.

[Satyajit-Chaudhuri]

So, I was trying to go ahead with [60, 70, 80, 90]. That also ended up throwing error. So what are the default quantiles - [80,90] only?