tools: scope sizelint glob off sepwork intermediates (#17)

sizelint's find globbed sepwork build intermediates (e.g. *.unit.ww)
mid-regen, causing spurious failures under parallel load (impl-f32 and
impl-speed both hit it). Prune *.sepwork dirs from the source glob;
tracked-source coverage unchanged.

tools/sizelint

@@ -33,6 +33,7 @@ files=$(find cmd selfhost lib \
 	\( -type d -name .git -prune \) -o \
 	\( -type d -name .claude -prune \) -o \
 	\( -type d -name .ai -prune \) -o \
+	\( -type d -name '*.sepwork' -prune \) -o \
 	\( -type f \( -name '*.c' -o -name '*.h' -o -name '*.ww' \) \
 		! -name '*.combined.ww' -print \) )