Fix: Resolve Android cross-compilation failure (Issue #458)

[dyrpsf]

Fixes #458.

The Problem:
When users attempt to compile h3-py for Android using Buildozer / python-for-android, the build fails at runtime with ImportError: dlopen failed: ... is for EM_X86_64 (62) instead of EM_AARCH64 (183).
Because p4a relies on standard pip install without explicitly passing a CMake toolchain file to scikit-build-core, CMake defaults to building host binaries (x86_64) instead of respecting the target NDK environment.

The Solution:
Added a minimal, non-intrusive environment check in the root CMakeLists.txt just before the project() declaration. If the standard $CC environment variable contains android (which is standard behavior for python-for-android), it automatically sets CMAKE_SYSTEM_NAME to Android.

This forces CMake into cross-compilation mode, allowing it to correctly link against the ARM64 Android NDK without interfering with standard desktop builds (Linux/Mac/Windows).