Fix TextIO import error

[qthibeault]

When using Python versions >= 3.12, importing RTAMT produces the following error:

Traceback (most recent call last):
  File "/home/runner/work/psy-taliro/psy-taliro/examples/f16.py", line 13, in <module>
    from staliro.specifications import rtamt
  File "/home/runner/work/psy-taliro/psy-taliro/src/staliro/specifications/rtamt.py", line 6, in <module>
    from rtamt import StlDenseTimeSpecification, StlDiscreteTimeSpecification
  File "/home/runner/.local/share/hatch/env/virtual/psy-taliro/dEx5JRFg/psy-taliro/lib/python3.13/site-packages/rtamt/__init__.py", line 5, in <module>
    from rtamt.spec.stl.discrete_time.specification import StlDiscreteTimeSpecification
  File "/home/runner/.local/share/hatch/env/virtual/psy-taliro/dEx5JRFg/psy-taliro/lib/python3.13/site-packages/rtamt/spec/stl/discrete_time/specification.py", line 3, in <module>
    from rtamt.syntax.ast.parser.stl.specification_parser import StlAst
  File "/home/runner/.local/share/hatch/env/virtual/psy-taliro/dEx5JRFg/psy-taliro/lib/python3.13/site-packages/rtamt/syntax/ast/parser/stl/specification_parser.py", line 2, in <module>
    from rtamt.syntax.ast.parser.stl.parser_visitor import StlAstParserVisitor
  File "/home/runner/.local/share/hatch/env/virtual/psy-taliro/dEx5JRFg/psy-taliro/lib/python3.13/site-packages/rtamt/syntax/ast/parser/stl/parser_visitor.py", line 4, in <module>
    from rtamt.antlr.parser.stl.StlParserVisitor import StlParserVisitor
  File "/home/runner/.local/share/hatch/env/virtual/psy-taliro/dEx5JRFg/psy-taliro/lib/python3.13/site-packages/rtamt/antlr/parser/stl/StlParserVisitor.py", line 2, in <module>
    from antlr4 import *
  File "/home/runner/.local/share/hatch/env/virtual/psy-taliro/dEx5JRFg/psy-taliro/lib/python3.13/site-packages/antlr4/__init__.py", line 5, in <module>
    from antlr4.CommonTokenStream import CommonTokenStream
  File "/home/runner/.local/share/hatch/env/virtual/psy-taliro/dEx5JRFg/psy-taliro/lib/python3.13/site-packages/antlr4/CommonTokenStream.py", line 33, in <module>
    from antlr4.Lexer import Lexer
  File "/home/runner/.local/share/hatch/env/virtual/psy-taliro/dEx5JRFg/psy-taliro/lib/python3.13/site-packages/antlr4/Lexer.py", line 12, in <module>
    from typing.io import TextIO
ModuleNotFoundError: No module named 'typing.io'; 'typing' is not a package

The typing.io module was deprecated in Python 3.8 and was scheduled for removal in 3.12, and the types were moved into the base typing module as of Python 3.6. The current usage of typing.io in some RTAMT modules means that newer versions of Python are not supported.

This fix adds a guard that selects the correct import for the TextIO type depending on the version reported by sys.version_info. This approach was chosen rather than just fixing the import to maximize backward compatibility, since the library currently indicates that it supports Python versions earlier than 3.6.