feat: selection Coordinate and weighted distance

tests/test_selection.py

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+import math
+
+import pytest
+
+from hef.catalog import Record
+from hef.selection import Coordinate, Weights, distance, record_coordinate
+
+
+def make_record(**overrides):
+    base = dict(
+        id="r",
+        title="t",
+        source_url="u",
+        source_archive="internet_archive",
+        license="public_domain",
+        mode="video",
+        left=0,
+        right=0,
+        dark=0,
+        light=0,
+        duration_s=600,
+        file_path="/media/r.mp4",
+    )
+    base.update(overrides)
+    return Record(**base)
+
+
+def test_distance_zero_for_same_point():
+    c = Coordinate(2, 2, 2, 2)
+    assert distance(c, c) == 0.0
+
+
+def test_distance_is_euclidean_by_default():
+    a = Coordinate(0, 0, 0, 0)
+    b = Coordinate(1, 1, 1, 1)
+    assert distance(a, b) == pytest.approx(2.0)  # sqrt(1+1+1+1)
+
+
+def test_weights_scale_planes_independently():
+    a = Coordinate(0, 0, 0, 0)
+    brain_only = Coordinate(1, 0, 0, 0)
+    mood_only = Coordinate(0, 0, 1, 0)
+    w = Weights(brain=4.0, mood=1.0)
+    assert distance(a, brain_only, w) == pytest.approx(2.0)   # sqrt(4*1)
+    assert distance(a, mood_only, w) == pytest.approx(1.0)    # sqrt(1*1)
+
+
+def test_record_coordinate_extracts_axes():
+    record = make_record(left=1, right=2, dark=3, light=4)
+    assert record_coordinate(record) == Coordinate(1, 2, 3, 4)