Feature: tier XI compatibility

Prepares BlitzKit for tier XI tanks ahead of their release. Tier X was hardcoded as the maximum in the tank search filters, the guesser and the tech tree, and had no roman numeral beyond X.

- Added `XI` to `TIER_ROMAN_NUMERALS`
- Added an awaitable tier list derived from the highest tier in the tank definitions, so nothing changes until tier XI tanks exist
- Used it for the tank search tier filters and the guesser tier picker and defaults
- Made the tech tree check for successors instead of assuming tier X is the last tier

Fixes #302

packages/website/src/components/Tankopedia/TechTreeSection/index.tsx

@@ -191,7 +191,7 @@ export function TechTreeSection({ skeleton }: MaybeSkeletonComponentProps) {
             );
           })}
 
-          {master.tier < 10 && (
+          {master.successors.length > 0 && (
             <>
               <Arrow />
               {master.successors!.map((id, index) => (