Add frame aware advance gate

[11EJDE11]

To advance a frame, Wait_For_Players currently checks their[i].recv >= their[i].sent. If a peer is behind on that count, the game stalls, even if the missing commands are for future frames and MaxAhead still allows simulation to continue.

This PR replaces the count-based check with a frame-aware one. A peer is considered caught up once all commands for frames <= current are known to have been received, based on each packet's (Frame, cumulative count) stamp.

In practice, this lets the game continue for a few more frames instead of stalling immediately. If the delayed packet arrives before those frames are reached, the stall is avoided entirely.

Also fixes a bug found along the way: CommandCountStalls was writing to the wrong per-peer index under packet loss, corrupting and unrelated frame-timing accumulator.

I've tested a few games. 3 players, 1 with 20% drop (using Clumsy) in/out.

Build	Effective FPS
Baseline (current implementation)	11.6-12.6
With this change	14.7-15.8

So not huge savings, but in my testing with a < 5000 frame game, there were about ~50 times this kicked in.

---

Vanilla:

With this PR:

Draft until Phobos-developers/YRpp#75

[github-actions]

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