fix: handle unsupported architectures gracefully in setup_env.py

[aayushbaluni]

Summary

Fixes three error-handling bugs in setup_env.py that cause crashes or misleading exit codes on unsupported platforms.

Bug 1 — exit(0) on error condition (line 212):
compile() calls exit(0) when the architecture is unsupported, reporting success instead of failure.

Bug 2 — ARCH_ALIAS KeyError on unrecognized platforms (line 85):
system_info() uses a dict lookup ARCH_ALIAS[platform.machine()] which raises KeyError for architectures not in the alias table (e.g. i686, riscv64, ppc64le). This crashes before the architecture check in compile() can provide a proper error message.

Bug 3 — parse_args() KeyError on unsupported arch (line 225):
parse_args() uses SUPPORTED_QUANT_TYPES[arch] for argparse choices, which also raises KeyError for unknown architectures.

Changes

• setup_env.py:85: Changed ARCH_ALIAS[platform.machine()] to ARCH_ALIAS.get(platform.machine(), platform.machine()) — unknown architectures now pass through instead of crashing.
• setup_env.py:212: Changed exit(0) to sys.exit(1) — error condition now reports failure correctly.
• setup_env.py:225-228: Added early arch check in parse_args() with a clear error message before argparse tries to use the unsupported arch.

Testing

• Known architectures (AMD64, x86_64, aarch64, arm64, ARM64) behave identically to before
• Unknown architectures now get a clear error message instead of an unhandled KeyError traceback
• All changes are backward-compatible with existing supported platforms
• No unrelated changes included

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