Adjust Slinger ranged attack to remove Knockback

[odecay]

Description

Change the knockback time and velocity for Slinger ranged attack to interrupt player for less time. Currently its very easy to become stunlocked by the Slingers projectile attacks.

Currently a thrown items attack velocity is determined by a const here

punchy/src/item.rs

Line 161 in b6ff6a9

 velocity: Vec2::new(consts::ITEM_ATTACK_VELOCITY, 0.0) * direction_mul, 

but this should be configurable per item.
This attack velocity is then used to determine HitStun velocity.

I also propose that we change the name of Attack.velocity and HitStun.velocity to Attack.pushback and HitStun.pushback to increase clarity of intended purpose.

[Isaac Turci]

I'll claim this