[Repo Assist] fix(bootstrap_refuter): fix 3 bugs in categorical/integer variable perturbation

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Three bugs in _refute_once() in dowhy/causal_refuters/bootstrap_refuter.py affecting any run that sets required_variables (i.e. uses the chosen_variables path):

Bug 1 — Integer dtype check evaluates incorrectly (line 113)

# Before (broken): Python evaluates "float" or "int" as "float" (truthy short-circuit)
if ("float" or "int") in new_data[variable].dtype.name:

# After (correct)
if "float" in new_data[variable].dtype.name or "int" in new_data[variable].dtype.name:
```

`("float" or "int")` is a valid Python expression but evaluates to `"float"`. Integer dtypes (`int32`, `int64`, `uint8`, ...) do not contain `"float"`, so integer common-cause columns silently received no noise during refutation — the refutation was meaningless.

## Bug 2 — `NameError` in the category branch (line 129)

`probs` was only defined inside `elif "bool"`. If the first categorical variable processed did not come after a boolean one, reaching `elif "category"` raised:

```
NameError: name 'probs' is not defined

Fix: define probs = np.random.uniform(0, 1, sample_size) at the start of the elif "category" block.

Bug 3 — 2-arg np.where + discarded astype (lines 129–130)

# Before: np.where with 2 args raises ValueError
new_data[variable] = np.where(probs < probability_of_change, changed_data)
# Also: astype returns a new Series, so this is a no-op:
new_data[variable].astype("category")

# After (correct):
new_data[variable] = np.where(probs < probability_of_change, changed_data, new_data[variable])
new_data[variable] = new_data[variable].astype("category")

np.where(cond, x) with only 2 positional args raises ValueError: either both or neither of x and y should be given. The 3rd argument (the "keep-original" array) was missing. Additionally, Series.astype() returns a new object and was not assigned back, leaving the dtype unchanged.

Tests

Two new regression tests in tests/causal_refuters/test_bootstrap_refuter.py:

Test	What it checks
test_integer_column_receives_noise	Integer dtype columns are actually perturbed (Bug 1)
test_categorical_column_no_crash	Category branch completes without NameError or ValueError (Bugs 2 & 3)

Test Status

black --check ✅ isort --check ✅ flake8 — pre-existing E501 in test file unchanged, no new errors introduced.

CI blocked pending maintainer approval of bot PR — tests could not be executed in this environment (no Poetry/venv), but all fixes have been verified by code inspection against the exact error paths described above.

Note: Bug 1 and the astype part of Bug 3 were also identified in PR #1633. This PR fixes all three bugs in one pass and supersedes #1633.

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