safe_eval rewrite_np does not actually wrap constants in numpy types

[chhayankjain]

Describe the bug

safe_eval(..., rewrite_np=True) is intended to wrap int/float literals in numpy types (e.g. np.int32) to prevent denial-of-service via slow native-Python exponentiation. Two bugs make this protection completely ineffective:

1. _RewriteConstNp.visit_Constant calls ast.parse(...) which returns an ast.Module node, but visit_Constant must return an ast.expr node. This corrupts the AST tree.
2. safe_eval evaluates the original string (eval(expr, ...)) instead of the rewritten AST, so the numpy-wrapping is silently discarded.

Additionally, the docstring on line 77 has a typo: "expressoini" should be "expression".

To Reproduce

import numpy as np
from monai.utils import safe_eval

# rewrite_np should produce numpy types, but returns native Python types
result = safe_eval("2 + 3", rewrite_np=True)
print(type(result))  # <class 'int'> — expected np.int32

# DoS protection is ineffective: this hangs under native Python int
# but should overflow instantly under np.int32
result = safe_eval("9**9**9", rewrite_np=True)
print(type(result))  # <class 'int'> — expected np.int32

Expected behavior

With rewrite_np=True, all int/float literals should be wrapped in the specified numpy types and the rewritten AST should be evaluated. safe_eval("2 + 3", rewrite_np=True) should return np.int32(5), not Python int(5).

Environment

MONAI version: 1.6.0rc1+53.g43c0aaed (includes PR #8936)

Additional context

Introduced in #8936. The existing tests pass because they only check numerical equality (assertEqual), not that the result type is actually numpy.

The call site in monai/bundle/scripts.py:168 relies on rewrite_np=True to prevent DoS attacks via bundle config expressions, so this is a security gap.

I have a fix and regression tests ready — opening a PR shortly.