Style cleanup in xrspatial/proximity.py (flake8 F841/E128, isort, mutable default)

[brendancol]

A style audit of xrspatial/proximity.py using the project's configured flake8 (max-line-length=100) and isort (line_length=100) settings turned up four issues. None of them break correctness on their own, but two touch runtime semantics, so it makes sense to fix them in one pass.

flake8 F841: dead local (line 1274)

original_chunks = raster.data.chunks is assigned in the unbounded dask+cupy branch and never read. It is a refactor leftover from when chunk geometry was restored after the cupy-to-numpy conversion. Remove it.

Mutable default argument (lines 1347, 1490, 1630)

The three public functions proximity, allocation, and direction declare target_values: list = []. A mutable default is shared across all calls. The current code never mutates it, so there is no live bug, but the pattern is fragile. Switch to a None sentinel and normalize to [] inside the body so behaviour stays identical.

flake8 E128: continuation line under-indent (line 291)

The nested np.where in _vectorized_calc_direction is under-indented for the visual indent. Reflow it.

isort: import ordering (lines 27-32)

The three from xrspatial... imports are not in the order isort expects under line_length=100. Re-sort.

Scope

• No behavioural change for the E128 reflow or the isort reordering.
• The F841 removal deletes dead code only.
• The mutable-default fix preserves behaviour (None normalizes to []).
• No flake8 or isort config changes, no autoformatter.

After the fix, flake8 xrspatial/proximity.py and isort --check-only xrspatial/proximity.py should both pass clean.