Function registerLeague

registerLeague(league: string, adapters: AdapterTable): void
Register an adapter table for a league. League keys are normalized to uppercase. Re-registering replaces the existing table.

To support a new sport:
1. Add the relevant prop keys to DfsPropTypeKey and aliases.
2. Build an AdapterTable mapping prop keys to extractor functions.
3. Call registerLeague('YOUR_LEAGUE', YOUR_ADAPTERS).
Parameters
- league: string
- adapters: AdapterTable
Returns void
Example
```
registerLeague('EPL', {
    'Goals': (entry) => parseInt(entry.points, 10) || 0,
  });
```
- Defined in stat-adapters/index.ts:67