0.2.51.21 (EXPERIMENTAL) - Clutch braking driver behaviour rewrite — Sprocket Steam update #139316

Hi all, Here's a full rewrite of clutch braking driver behaviour for the movement overhaul on the experimental branch. Allows for more complex behaviours like speed matching while shifting, as well as cleaning it up on my end. Changes Reduced leaf spring stiffness by 1/3. Clutches are no longer engaged linearly, now following an easeInOutCubic curve. Made steering clutch speed faster. The driver now speedmatches during shifts. The driver no longer upshifts until it's been 2.0s until the last steer input. So the driver will be less likely to shift while manoeuvring. Greatly reduced engine friction. Improves coasting. The driver no longer downshifts during coasting. Improves coasting. Fixed braking not applying correctly at high speeds. The driver now launches in 2nd gear on flat terrain. This was more common than starting in first. Fixed suspension instability and flipped arms on torsion ...