Players can sometimes join beyond the table limit

[sleepyfoxen]

Describe the bug

• If several people sit at once, the table limit isn't enforced and players may take seats above the limit.
• Then, the button to stand is greyed out and can't be clicked.

To Reproduce
Steps to reproduce the behavior:

1. Create a room with a player limit
2. Fill the table, leaving a single seat empty
3. Have several people try to sit at the same time

Expected behavior
The table limit should be enforced -- additional players above the limit should be prevented from sitting.

Screenshots

Desktop (please complete the following information):

• OS: Linux (Ubuntu LTS 20.04, kernel 5.4.0-62-generic)
• Browser: Tor Browser 10.0.8 (based on Mozilla Firefox 78.6.1esr) (64-bit)

Additional context
Actions could be implemented as atomics, guaranteeing a strict total order of events.

[caracolplusplus]

Ive learned that atomic arrays can be controlled on beforeSave hooks

We can clamp the length of the array there