v2.1.0

• feat: update sdk constraint to v2.12.0 stable
• feat: additional lint rules:
  • avoid_print
  • avoid_returning_null_for_void
  • avoid_single_cascade_in_expression_statements
  • avoid_unnecessary_containers
  • avoid_web_libraries_in_flutter
  • curly_braces_in_flow_control_structures
  • exhaustive_cases
  • file_names
  • no_logic_in_create_state
  • prefer_const_constructors_in_immutables
  • prefer_const_declarations
  • prefer_const_literals_to_create_immutables
  • prefer_function_declarations_over_variables
  • prefer_inlined_adds
  • prefer_is_not_operator
  • prefer_null_aware_operators
  • prefer_void_to_null
  • provide_deprecation_message
  • sized_box_for_whitespace
  • unnecessary_overrides
  • unnecessary_string_escapes
  • unnecessary_string_interpolations
  • use_full_hex_values_for_flutter_colors
  • void_checks