Encirclement does not work on map edges

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**Describe the bug**
So far I am aware of this strategy/feature "encirclement": if player A's land fully surrounds player B's land (NPC or not), then player B instantly loses and the land becomes owned by player A.

However, this does not work on map edges.

**To Reproduce**
Steps to reproduce the behavior:

1. Start near map edge (Player A)
2. Find a player that is at the map edge (Player B)
3. Surround Player B
4. No encirclement is triggered

**Expected behavior**
Encirclement should occur and Player B loses.

**Screenshots**
(Not screenshot, but an illustration of the situation.)

Consider this hypothetical scenario, where the colors are:
- White: unowned/neutral
- Red: Player A
- Blue: Player B
- Black: out-of-bounds area / map edge

Then, Player A should have encircled Player B, and Player B should lose.

**Desktop (please complete the following information):**

- OS: Windows
- Browser: Firefox
- Version 152

**Additional context**

It may be a good idea to also check lake-side / ocean-side encirclement, to ensure encirclement still works as expected.

**Assignment**

- [ ] I'd like to be assigned to this issue and work on it myself

Commencez par reproduire le scénario en bordure de carte décrit dans l’issue, puis comparez-le à un encerclement près d’un lac ou de l’océan. Suivez la vérification de l’encerclement depuis le point d’entrée du gameplay ; le travail est terminé lorsqu’un joueur complètement encerclé au bord de la carte perd et que la propriété change, tandis que le comportement existant hors bordure reste correct.

Rédigé par le modèle d'indexation à partir du texte de l'issue.