Run Black formatter on codebase

[Copilot]

Applied Black formatter to entire Python codebase per maintainer request.

Changes:

• Reformatted src/eigenscript/compiler/codegen/llvm_backend.py with trailing commas and line formatting improvements
• 66 files already compliant, no changes needed

# Before
raise CompilerError(
    f"Function '{mangled_name}' not found",
    hint=f"Make sure module '{module_name}' is imported and compiled first",
    node=node
)

# After
raise CompilerError(
    f"Function '{mangled_name}' not found",
    hint=f"Make sure module '{module_name}' is imported and compiled first",
    node=node,
)

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