Adjust default MLH settings and unhide options for next release.

[AlexisOlson]

Having hidden options that are set to not-recommended defaults is a major usability issue.

The defaults here still have MLH disabled but only require changing two parameters to match the settings recommended by the current !mlh bot command on Discord:

MovesLeftMaxEffect 0.15
MovesLeftThreshold 0.3
MovesLeftSlope 0.015
MovesLeftQuadraticFactor 1.0
MovesLeftConstantFactor 0.0
MovesLeftScaledFactor 0.0

[Naphthalin]

The above values were tuned for 0.07 slope for T70, which now uses a sharper slope so whenever this is relevant, policies should already be sharper. I therefore would prefer slope=0.01 as the default value and not higher. Default threshold should be 0.99 or so so it would be off by default (until terminal nodes), and to activate it we only need to reduce the threshold. Also, I am strongly against unhiding the 3 factors, once we have reasonable default values. These were only intended to adjust the Q curve without having to change the binary.

[AlexisOlson]

A different slope is fine. We can adjust to whatever is considered best when it comes time to merge.

I left the threshold at 1.0 because since MLH is disabled by default, the do_moves_left_adjustment boolean should be false to prevent unnecessary calculation of M_effect. It might make sense to add an m_cap > 0.0 condition in the definition of do_moves_left_adjustment. Then we could set a default threshold of less than 1.0 without triggering do_moves_left_adjustment when m_cap = 0 (and you'd only need to adjust one parameter to use MLH with recommended settings).

Long term, hiding the 3 factors is fine but they should be unhidden as long as there isn't a clear consensus on their settings. It's not clear to me whether or not we have that consensus yet. If there is consensus, I'm fine with keeping them hidden.

[mooskagh]

I'm not sure about unhiding part, especially given that there will be an easier way to unhide all hidden params ("pro version").
Actually, I'm more for hiding more parameters that most of people don't touch. There were multiple complaints about that including from top chess players.

[AlexisOlson]

Hidden is fine as long as they don't need tweaking for best results.

However, it seems like best results for the factor settings aren't completely settled yet:
https://discord.com/channels/425419482568196106/530486338236055583/719100480885751808

[Naphthalin]

It seems like you pushed an old branch again, as the MLH options are unhidden again?

[AlexisOlson]

@Naphthalin No, I never re-hid them as it hasn't been clear which factor values should be the default. Is there a consensus that quadratic = 1 should be default with other options not directly accessible?

[Tilps]

I think we can argue about hide vs unhide while the RC process is going on - most important is the default values are improved.

Requested changes were applied and I'm approving as forward progress.