Support for `lazy` imports (PEP 810, Python 3.15+)

[cjw296]

Python 3.15 introduces PEP 810 - Explicit lazy imports via the new lazy soft keyword:

lazy import json
lazy from pathlib import Path

Currently mypy reports these as syntax errors. Support is needed to:

• Update the parser to recognise lazy import and lazy from ... import statements
• Treat lazy imports the same as regular imports for type checking purposes (as noted in PEP 810 § Typing and tools)

Related:

• Support and lints for lazy imports in Python 3.15+ astral-sh/ruff#21305 (ruff tracking issue)
• Support for lazy imports (PEP 810, Python 3.15+) astral-sh/ty#2968 (ty tracking issue)