Merge pull request #188 from gomlx/nans

v0.21.0: 2025/07/01 🌞 Summer Edition 🌞

Updated go version for docker.

Merge pull request #180 from gomlx/be_err

* Package `backends`:
  * **API BREAKING CHANGE**: Methods `backends.NewWithConfig()`, `xla.New()` and `simplego.New()` all changed,
    now they return also an error.
  * Method **`backends.New()` will be changed to return an error (as opposed to panic) at next version**.
    Temporarily the methods `MustNew()` (which panics on errors, like today) and `NewOrErr` (which returns
    an error) were created to have a clear API, and `New()` was marked as deprecated. 
  * Added `IsFinalized()` to the Backend API, to better handle attempts to access finalized backends.
  * Fixed bug in `xla` backend where an error was not being sent when Backend was already finalized.
* Package `types/tensors/numpy` with methods to read and write tensors from/to `.npy` and `.npz` files.
* Package `simplego`:
  * Fixed bug introduced in parallelize version of `Erf(x)`.
* Package `tensors`:
  * Added `Tensor.ToLocal()` to detach a tensor from its backend.
* Package `ui/gonb/plotly`: 
  * Update dependencies to new go-plotly v0.7.0 (many changes to the API), while preserving as much as possible
    the GoMLX api offered.
* Updated example notebooks to use `github.com/gomlx/gomlx/backends/default` (instead of only `/xla`) and to
  use the new `backends.MustNew()`.

Merge pull request #175 from gomlx/opt

Optimizations

Merge branch 'main' of github.com:gomlx/gomlx

Bumped version to v0.19.3

Version bump v0.19.2

Updated CHANGELOG and converage.

Bumped version; Fixed some typos.

Merge branch 'main' of github.com:gomlx/gomlx