Sd-mecha

- rename method `clip` to `clamp` to disambiguate it from "CLIP" the text encoder

- change default value of parameter `alpha` in `add difference` from `0.5` to `1.0`

- add module t5xxl to sd3 architecture

- add builtin support for architecture Stable Diffusion 3

- fix the handling of negative frequency buckets in `create_filter`
- remove the training loop in `create_filter`, which turned out to be causing issues. the naive cut approach appears to give less burnt out results
- rename parameter `mean` to `alpha` in `crossover` and `distribution_crossover` methods
- change default value of parameter `overlap` in `dropout` to `1.0`, since it is what people should expect by default in general
- optimize `overlap=1.0` in `dropout` to take linear space and time instead of exponential
- clear garbage collector and cuda memory when done merging. it seems to help with merging consecutively many models with a single script

- Minor fix: close safetensors files as soon as merging is completed.