Calculate rumple on the voxel grid

[iosefa]

Rumple now returns a raster on the same voxel grid as canopy cover, PAI, and FHD. Each cell uses canopy maxima and its eight neighbors to calculate surface area with the Jenness method.

Adds optional interpolation to fill missing canopy heights before calculating rumple. Use interpolation="linear", "cubic", or "nearest"; the default leaves gaps unfilled. Observed heights are preserved, and the height threshold still applies. This also works with tiled output, where larger gaps may need a wider buffer.

Includes tiled GeoTIFF output, docs, tests, and an updated notebook map. In the notebook, linear interpolation fills 30,499 missing rumple cells and increases coverage from 96.6% to 99.6%.

Validation: 152 tests passed, with one existing slow integration test skipped. CI passes on Python 3.11, 3.12, and 3.13. The notebook ran end to end and the docs built successfully.

Also updates the PDAL pin so CI keeps the installed 3.5.x bindings instead of downgrading to 3.4.5.

This overlaps #54, which uses a different calculation. This version builds the canopy surface from column maxima and uses the Jenness surface-area method.

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

✅ All modified and coverable lines are covered by tests.
❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Files with missing lines	Coverage Δ
pyforestscan/calculate.py	75.08% <100.00%> (+20.13%)	⬆️
pyforestscan/process.py	63.70% <100.00%> (+12.94%)	⬆️
tests/test_calculate.py	100.00% <100.00%> (ø)
tests/test_process.py	94.63% <100.00%> (+3.80%)	⬆️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.