DOC: Clarified the meaning of optional arguments in optimize.leastsq

[madphysicist]

https://stackoverflow.com/q/75278309/2988730 and my own experience indicate that the docs are not quite clear on this point

[ci skip]

[mdhaber]

Thanks! When gh-17878 merges, I'll go ahead and merge this.

@madphysicist as a follow-up, would you consider doing something like gh-17837 for curve_fit? With that change, curve_fit would return a bunch object instead of a plain tuple when full_output=False. The first two outputs can be unpacked (for backward compatibility), but the remaining return values would still be accessible as attributes. This would allow full_output to be deprecated.

If so, I'd suggest sending a message to the mailing list like this because public API changes need to be approved.