Allow railroad loops (#1274)

## Description:

This change enables loop formation in the station network, allowing for
enhanced connectivity. However, it can sometimes result in clustered
areas as a trade-off. To mitigate excessive clustering, loops are only
permitted when there are at least 5 intermediary stations between the
source and destination stations.


![image](https://github.com/user-attachments/assets/720fa4f9-a634-49e8-8027-fe4e244d5ae5)

Also a few fixes for `.dev` players.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

src/client/graphics/layers/UnitInfoModal.ts

@@ -246,7 +246,10 @@ export class UnitInfoModal extends LitElement implements Layer {
             class="upgrade-button"
             title="${translateText("unit_info_modal.create_station")}"
             style="width: 100px; height: 32px;
-              display: ${this.unit.hasTrainStation() ? "none" : "block"};"
+              display: ${this.unit.hasTrainStation() ||
+            !this.game.unitInfo(this.unit.type()).canBuildTrainStation
+              ? "none"
+              : "block"};"
           >
             ${translateText("unit_info_modal.create_station")}
           </button>