Fix rebinning of partially occupied histograms

[johannes-mueller]

Fix #234

[Copilot]

Pull request overview

Fixes #234 by correcting how rebin_histogram(..., binning=int) determines target binning for partially occupied MultiIndex (e.g., sparse 2D histograms), avoiding over-fine bins when rebinned.

Changes:

• Adjust rebin_histogram MultiIndex/int handling to compute a per-dimension “global” target IntervalIndex, then subset it per group to the occupied range.
• Update _do_rebin_histogram NaN handling by dropping NaNs once up-front (instead of per-interval).
• Add regression tests for fully/partially occupied 2D histograms (same/up/down) and document the fix in the changelog.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/pylife/utils/histogram.py	Fixes bin calculation for sparse MultiIndex histograms when binning is an int; adjusts NaN filtering and a binning validity edge case.
tests/utils/test_histogram.py	Adds regression coverage for sparse vs fully occupied 2D histograms across same/up/down rebin scenarios.
CHANGELOG.md	Notes the bug fix under upcoming release bug fixes.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

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[Copilot]

PEP 8 expects two blank lines between top-level function definitions. Please add an extra blank line before the new helper defs so formatting stays consistent with the rest of this module.

[Copilot]

The helper parameter name names_to_drop is misleading because the levels are not dropped; they are encoded to integer codes and later restored. Consider renaming it to something like names_to_encode/names_to_map to make the intent clearer.

Suggested change

	def _with_range_index(hist, names_to_drop):
	new_hist = hist.copy().reset_index(drop=False)
	for level in names_to_drop:
	def _with_range_index(hist, names_to_encode):
	new_hist = hist.copy().reset_index(drop=False)
	for level in names_to_encode:

[Copilot]

Typo in test name: histogam should be histogram for clarity and discoverability.

[Copilot]

Typo in test name: histogam should be histogram for clarity and discoverability.