Optionally return the dislocation core fit error.

[imaliyov]

Modified the fit_core_position() and fit_core_position_images() functions of the dislocation.py module.
return_error and return_errors flags added. If True, the functions will return the error of the scipy.optimize.minimize fit of the dislocation core position. This will require an additional cost_function() call. This probably can be avoided in the future if the error can be obtained directly from the minimize() function.

[jameskermode]

@pgrigorev or @thomas-rocke would one of you be willing to take a look at this PR?

[pgrigorev]

@jameskermode, we have already discussed this PR with Ivan, but I will have a closer look on the changes and let you know here.

[jameskermode]

The failing tests are due to an ASE change, which could be fixed here or in a separate PR. I think ase.neb has moved to ase.mep.neb.

[jameskermode]

We've also got some numpy 2 issues. I'll open an issue about that.

[pgrigorev]

ah I see. Yes we should fix that. I guess the best way would be to check ase version on import to keep backward compatibility?

[pgrigorev]

I think the tests failing tests have been fixed now, @imaliyov could you merge it to your branch?

[imaliyov]

@pgrigorev thank you, I have merged it to my branch.

[pgrigorev]

Everything looks good, I am sure it is safe to merge!

[pgrigorev]

Sorry it took so long, but after having a look on the changes I think it is safe to merge. (the changes are really minor)

[jameskermode]

Thanks!