fix(config): remove as Name re-export pattern to support PYTHON_LAZY_IMPORTS=all (Python 3.15)

[Tejas5405]

Problem

pytest crashes when run with Python 3.15's PYTHON_LAZY_IMPORTS=all environment variable:

$ PYTHON_LAZY_IMPORTS=all pytest --help
Traceback (most recent call last):
  File ".../src/_pytest/config/__init__.py", line 50, in <module>
    from .exceptions import UsageError as UsageError
ImportError: lazy import of '_pytest.config.exceptions.UsageError' raised an exception during resolution

Root cause

Python 3.15 introduces PYTHON_LAZY_IMPORTS (PEP 690) which defers module loading until names are first accessed. The from module import Name as Name pattern (where the alias repeats the original name) is a well-known mypy/pyright re-export marker — but it conflicts with the lazy import resolution mechanism in Python 3.15.

Lines 48–49 in src/_pytest/config/__init__.py use this pattern for PrintHelp and UsageError:

# Before — breaks PYTHON_LAZY_IMPORTS=all
from .exceptions import PrintHelp as PrintHelp
from .exceptions import UsageError as UsageError

Fix

Remove the redundant as Name alias. A # re-exported comment preserves the intent for human readers:

# After — compatible with PYTHON_LAZY_IMPORTS=all
from .exceptions import PrintHelp  # re-exported
from .exceptions import UsageError  # re-exported

This is a no-op at runtime. The only practical change is that strict-mode type checkers (mypy --no-implicit-reexport) will no longer treat these as explicit re-exports — but since _pytest.config is a private namespace, this is an acceptable tradeoff for Python 3.15 forward-compatibility.

Closes #14632