Relax Python requirement to >=3.8

Add missing from __future__ import annotations to _syscall_table.py
which used dict[str, int] at runtime (3.10+ only).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: congwang-mk

pyproject.toml

@@ -6,7 +6,7 @@ build-backend = "setuptools.build_meta"
 name = "sandlock"
 version = "0.1.0"
 description = "Lightweight process sandbox using Landlock, seccomp, and seccomp user notification"
-requires-python = ">=3.10"
+requires-python = ">=3.8"
 dependencies = ["tomli>=1.0; python_version < '3.11'"]
 license = {text = "Apache-2.0"}
 readme = "README.md"

src/sandlock/_syscall_table.py

@@ -8,6 +8,7 @@
 To regenerate from headers:
     grep -oP '#define __NR_(\w+)\s+(\d+)' /usr/include/.../unistd_64.h
 """
+from __future__ import annotations
 
 # fmt: off