fix(vyper): correct shift and division assignment operator mappings

[racequite]

Description

Fix incorrect Vyper AST operator mappings for shift operations and division assignment.

Previously, Vyper Shr and Shl were mapped to the opposite binary operators, so >> could be parsed as << and vice versa. The augmented assignment mapping had the same issue for >>= and <<=, and also mapped Div to -= instead of /=.

These operator strings are passed into BinaryOperationType.get_type() and AssignmentOperationType.get_type(), so the incorrect mapping could affect SlithIR generation and analyses that depend on arithmetic or bitwise semantics.

Changes

• Map Shr to >> and Shl to <<
• Map Div augmented assignment to /=
• Map Shr to >>= and Shl to <<=
• Add unit tests covering the affected Vyper operator mappings

Testing

python -m pytest tests/unit/vyper_parsing/test_ast.py -q

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