docs: summarize issue-095 cleanup

Author: basnijholt

CLEANUP.md

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+# ISSUE-095 cleanup summary
+
+This branch keeps the 1D `LearnerND` behavior from `issue-095-impl-py` and only
+refactors the implementation and tests for clarity.
+
+## What changed
+
+### `refactor: consolidate 1D cleanup tests`
+
+- Folded repeated 1D triangulation cases into parametrized tests.
+- Reused small helpers in the new 1D `LearnerND` unit tests instead of repeating
+  the same setup and tell/ask flow.
+- Consolidated the 1D and 2D integration smoke tests so the shared runner
+  behavior is checked in one place.
+
+Why: the original 1D test additions covered the right behavior but repeated a
+lot of setup and assertions, which made the cleanup surface harder to review.
+
+### `refactor: clarify 1D triangulation and interpolation`
+
+- Extracted `_flat_simplices()` so the 1D triangulation initialisation reads as
+  one explicit helper instead of an inline special-case loop.
+- Renamed local variables in `simplex_volume_in_embedding()` so the 2-vertex
+  branch and the embedding-dimension branch are easier to read.
+- Extracted `_sorted_line_data()` and `_plot_1d()` in `LearnerND` so the 1D
+  interpolation and plotting paths are short, named, and isolated.
+- Updated the `plot()` docstring to match the current 1D+2D behavior.
+
+Why: the 1D support is still a real special case, but these helpers make the
+special handling intentional and easier to follow without changing behavior.
+
+### `refactor: simplify DataSaver key reconstruction`
+
+- Replaced `_to_key(..., use_tuple=...)` with two small helpers:
+  `_mapping_uses_tuple_keys()` and `_row_to_key()`.
+- Switched `load_dataframe()` to inspect `self.learner.data` directly instead of
+  relying on `__getattr__` indirection.
+- Renamed `keys` to `input_columns` to match what the variable actually holds.
+
+Why: the 1D `LearnerND` DataFrame fix depends on whether the wrapped learner uses
+tuple keys for single inputs, and the new helper names make that rule explicit.
+
+## Guardrails kept
+
+- No public API changes.
+- No behavior changes intended.
+- Full `python -m pytest adaptive/tests/ -x --no-cov` runs were used to verify
+  each cleanup slice before it was committed.