Modify the difficulty multiplier from 1.25x to 0.75x for sen to better match expected SR value

[ziv-vy]

Until sen gets an actual SR calc (which could take years), I think that this value should be changed to something better. Currently, the value is very inflated and makes no real sense when compared with any other ruleset (despite the fact that this ruleset has many similarities with std and skill transfers relatively easily).
To get to the 0.75x value, I have referenced this spreadsheet, where I set 24 plays on std and stki.
Sorry egos.

Related: #188, #701

[LumpBloom7]

The SR multiplier was chosen in context of converts being the primary source of maps, where by nature of "throwing shit at the wall", would lead to some maps (like high SR maps) being ridiculously difficult. The SR multiplier is an attempt to not underrepresent such cases, with the obvious tradeoff.

For lower SR maps, this multiplier impacts less than it would on higher SR.

Even ignoring the above, a reduction of multiplier makes little sense.

_{Jokes aside, the original inline comment still demonstrate a good reason to do what I did.}

[ziv-vy]

Alright then, understandable.