Fix uv sync for some MacOS Systems

[jeff-hykin]

On MacOS a python executable can be "universal" (one file for both x86 and arm). The python executable for the uv python action on github runners (and on many normal MacOS installs) is universal. In our setup.py, we add C-compiler optimization arguments (e.g. -march=native). This causes uv sync to break because clang can only perform that optimization if it targets specifically arm64 xor x86 MacOS (can't do it when targeting for MacOS's universal executable format). The setup.py keeps the optimization whenever possible.

[greptile-apps]

Greptile Summary

Fixes uv sync failures on MacOS systems with universal Python binaries by detecting universal binaries and conditionally excluding the -march=native compiler flag, which clang doesn't support for multi-architecture targets.

Key changes:

• Adds python_is_macos_universal_binary() function to detect MacOS universal (fat) binaries by reading Mach-O header magic numbers
• Conditionally applies -march=native optimization only when not building against a universal binary
• Pins drake==1.45.0 specifically for MacOS (non-aarch64) while keeping drake>=1.40.0 for other platforms

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The implementation correctly detects MacOS universal binaries using standard Mach-O magic numbers, gracefully falls back on errors, and preserves optimizations for non-universal builds. The drake version pinning is isolated to MacOS.
• No files require special attention

Important Files Changed

Filename	Overview
setup.py	Adds universal binary detection to conditionally exclude -march=native flag on MacOS, preventing clang compilation errors
pyproject.toml	Pins drake==1.45.0 for MacOS (non-aarch64) and keeps drake>=1.40.0 for other platforms
uv.lock	Lock file updated to reflect drake version pinning and platform-specific dependency resolution

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[setup.py execution] --> B{Check Python executable}
    B --> C[Read binary header]
    C --> D{Is Mach-O universal binary?}
    D -->|Yes: FAT_MAGIC detected| E[Use base compile flags only]
    D -->|No: Single arch or non-MacOS| F[Add -march=native flag]
    E --> G[extra_compile_args = -O3, -ffast-math]
    F --> H[extra_compile_args = -O3, -ffast-math, -march=native]
    G --> I[Build C++ extension]
    H --> I
    I --> J{Clang compilation}
    J -->|Universal binary + -march=native| K[ERROR: Incompatible flags]
    J -->|Single arch or no -march=native| L[SUCCESS: Extension built]

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