Release 1.4.0: PDN mode, the config-file workflow, and the dialog editor

Multiple Thevenin supplies and prescribed-current loads on one net,
solved in absolute volts with the Tellegen power balance verified per
run; a source-sink pair table (effective copper resistance per
supply x load pair plus an exactly-summing proportional-sharing loss
attribution), in summary.txt and as its own figure. Bonded terminals
short a package's contacts into one lug so the per-pin split becomes
a solve outcome. Geometry dumps carry the terminal set (schema v8).

The dialog gained a Classic/PDN mode selector and a full PDN editor:
per-role supply/load tables built from the marker rectangles (or a
config's terminal set, which never pins mode or net), with Component
hints, per-terminal Layer scopes, Active checkboxes, comments, a
per-net row filter, resizable tables and a scrolling, screen-sized
dialog. Numbers accept SI suffixes (50m, 4.7k) everywhere.

fill_res_config.json fully specifies a run (classic or PDN) with
validation, comments, named side-by-side configs (the one called
default auto-loads), Load/Save buttons with an editable file name,
and saves that never drop anything drawn on the board.

347 tests, green on Python 3.13 and on the 3.9 macOS wheel stack.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_skin.py

@@ -122,3 +122,27 @@ def test_dc_default_unchanged():
     assert res.freq_hz == 0.0
     assert res.skin_depth_um is None
     assert all(r == 1.0 for r in res.rs_ratios)
+
+
+@pytest.mark.parametrize("text, value", [
+    ("50m", 0.05), ("4.7k", 4700.0), ("2M", 2e6), ("10", 10.0),
+    ("3,3", 3.3), ("1,5k", 1500.0), ("500u", 5e-4), ("2µ", 2e-6),
+    ("100n", 1e-7), ("1p", 1e-12), ("1G", 1e9), ("4K", 4000.0),
+    ("50 m", 0.05), ("-2m", -0.002), ("1e3", 1000.0), ("0", 0.0),
+])
+def test_parse_engineering_values(text, value):
+    assert skin.parse_engineering(text) == pytest.approx(value, rel=1e-12)
+
+
+@pytest.mark.parametrize("bad", ["", "m", "junk", "5k5", "1,500k",
+                                 "1.2.3", "50 m m"])
+def test_parse_engineering_rejects_garbage(bad):
+    with pytest.raises(ValueError):
+        skin.parse_engineering(bad)
+
+
+def test_parse_engineering_case_separates_milli_from_mega():
+    # exactly the trap parse_frequency sidesteps by lowercasing: for
+    # general values 50m and 50M are 9 orders of magnitude apart
+    assert skin.parse_engineering("50m") == pytest.approx(0.05)
+    assert skin.parse_engineering("50M") == pytest.approx(5e7)