Simple Upgradable Structures (Cities, Ports, SAMs and Silos) (#1012)

## Description:

https://github.com/openfrontio/OpenFrontIO/issues/776

I've implemented upgradable structures for cities and ports.

As of right now this is just meant as a QOL change for structure
stacking that currently happens and no gameplay changes are intended.

Structure upgrades cost the same as making a new structure of that type
and function the same as making a new structure of that type.

I'm putting up a draft PR for this now since adding support for SAMs and
Silos will take more time to handle the cooldowns and I want to make
sure I'm on the right track for getting this merged.

I also still need to add bot behavior for this and re-enable min
distance for structures.

I didn't see translations for the UnitInfoModal so I've left that out
for now.

I've tested locally in a single player game so far but will document and
test more thoroughly before merging.


![image](https://github.com/user-attachments/assets/321a17cf-26a5-4152-aae1-6b6a691638bb)


![image](https://github.com/user-attachments/assets/8cfdabe6-f0a1-435a-a5a3-05b442427c2f)


## 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

## Please put your Discord username so you can be contacted if a bug or
regression is found:

# Poutine

---------

Co-authored-by: Scott Anderson <scottanderson@users.noreply.github.com>

src/core/game/PlayerImpl.ts

@@ -754,6 +754,12 @@ export class PlayerImpl implements Player {
     return b;
   }
 
+  upgradeUnit(unit: Unit) {
+    const cost = this.mg.unitInfo(unit.type()).cost(this);
+    this.removeGold(cost);
+    unit.increaseLevel();
+  }
+
   public buildableUnits(tile: TileRef): BuildableUnit[] {
     const validTiles = this.validStructureSpawnTiles(tile);
     return Object.values(UnitType).map((u) => {