…nt configurations

Allow RediSearchSchema to accept an array of field definitions for a single field,
enabling the same field to be indexed with different types and aliases.

Example:
```typescript
{
  sku: [
    { type: SCHEMA_FIELD_TYPE.TEXT, AS: 'sku_text' },
    { type: SCHEMA_FIELD_TYPE.TAG, AS: 'sku_tag', SORTABLE: true }
  ]
}
```

- Add SchemaFieldDefinition type for reusable field type union
- Update RediSearchSchema to accept SchemaFieldDefinition | SchemaFieldDefinition[]
- Update parseSchema to normalize input and iterate over field definition arrays

---

- fix typo in PT SCHEMA_TEXT_FIELD_PHONETIC

- Add JSDoc and README documentation for the new array syntax that allows
indexing the same field multiple times with different types or aliases.