Strategy deduplication performance issue and incorrect handling of empty tuple schemas

[Bitshifter-9]

1. Performance issue: O(n²) strategy deduplication in _MetaSchemaBuilder
   Location: genson/schema/builder.py url:https://github.com/wolverdude/GenSON/blob/master/genson/schema/builder.py
   Current behavior:
   schema strategies are deduplicated using a list with repeated membership checks,
   This results in O(n²) time complexity

           unique_schema_strategies = []
           for schema_strategy in schema_strategies:
               if schema_strategy not in unique_schema_strategies:
                   unique_schema_strategies.append(schema_strategy)

2.Bug: Empty tuple schemas produce an unexpected schema item
Location: genson/schema/strategies/array.py url:https://github.com/wolverdude/GenSON/blob/master/genson/schema/strategies/array.py
Steps to reproduce

  from genson import SchemaBuilder
  builder = SchemaBuilder()
  builder.add_schema({'type': 'array', 'items': []})
  schema = builder.to_schema()
  

current output:{'type': 'array', 'items': [{}]} Expected output:{'type': 'array', 'items': []}

The Tuple strategy initializes its internal _items list with a single empty schema instance, even when the tuple definition is explicitly empty.