Investigate using sv_fps 40 as a default

[Calinou]

Similar to what I proposed in etlegacy/etlegacy#2555, WoP would benefit to defaulting to a higher tickrate by default for smoother, low-latency gameplay. Both local matches and public servers would benefit from this change:

• Other players' movement follow more closely the player's actual position. Since hitscan weapon effects are not predicted, a noticeable delay between clicking the left mouse button and hitting a player due to the tick rate. This also reduces peeker's advantage by design.
• Being pushed around by other players is smoother (or at least less frustrating 😛).
• Local bot matches feel smoother, with less delay when firing weapons.
• Spectating a player looks more accurate to their true actions.
• The floater operates more smoothly (sudden velocity changes don't cause visible teleporting of your character anymore).

In terms of CPU/bandwidth requirements, I'd expect most public servers to be able to run sv_fps 40 without trouble.

The main difficulty would be to handle cases where the game logic has sv_fps-dependent behavior, but I didn't find too many from testing so far. The main issue I found was that floater speed depends on sv_fps, with higher values resulting in slower acceleration (making the floater's effect weaker). It's especially noticeable at sv_fps 125 where the floater barely has any effect (and can't take you off the ground), but at sv_fps 40, it mostly makes a difference when you use the floater to try to reverse a hard fall.

• Edit: The floater issue was fixed by f75a078.

Note that if we carry over this change, it would be worth using cl_maxpackets 125 as a default as well to further improve smoothness and reduce jitter.

See my comment over on Xonotic's GitLab for even more detailed rationale. There are already several id Tech 3-based games defaulting to 40 Hz (Quake Live and Unvanquished) - let's try to make World of Padman another one of them 🙂