Confirm parameter setting with info string uci response

[mooskagh]

Currently we don't return anything on successful setparam set, and return error non-standart response in error.

It would be more visible in GUI if we used info string <text> in both cases.

[ErdoganSeref]

Is setparam a method in a source file? What <text> should we return?

[mooskagh]

Error is output in this line:

lc0/src/chess/uciloop.cc

Line 143 in ba24142

SendResponse(std::string("error ") + ex.what());

The setparam is handled here:

lc0/src/engine.cc

Line 350 in 86288ac

options_.SetUciOption(name, value, context);

[ErdoganSeref]

Fixed part of the issue with #1755.

[rooklift]

Is this necessary? I don't think other engines do this.

[mooskagh]

Other engines probably don't do that indeed, but I believe it makes sense to make errors more visible.

Most of GUIs will show info string messages to the user somehow instead of ignoring, and I think it good and I don't even see drawbacks. Do you see why it could be bad?

[rooklift]

I guess it will be fine, it's just I already have to parse info string lines for verbose move stats purposes, but I can probably ignore these.

Having said that, I think info lines are generally supposed to be sent during a search. I can't immediately predict what my own GUI will do when they come at other times, let alone other people's GUIs. [OK, I guess mine will ignore it.]

[mooskagh]

Actually, particularly for confirming that the command worked, it may be questionable whether it's good or bad.
But for reporting errors, I think has much more pros than cons.

I'm pretty sure that many engines use info string for various purposes outside of search, most frequently to output license/logo/etc at the startup.

Hold on with the changes though, there's another one coming in which may be useful, I hope to add jsoninfo response soon (work in progress here: https://github.com/mooskagh/lc0/tree/json) which should be much easier to parse.