Add datetime components 196-215; Kit.At; inert stepper arrows

Calendars, date and time inputs, pickers, clocks, timers, a sun dial,
a season wheel, an agenda and a day schedule. Kit.At rebuilds at a
moment (relative times, midnight). Stepper and NumberInput arrows stop
under Inert. DateInput parks a popup focus as its own.

datetime/yearpicker.go

@@ -0,0 +1,60 @@
+package datetime
+
+import (
+	"fmt"
+	"log/slog"
+	"strconv"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type YearPickerOptions struct {
+	Disabled bool
+}
+
+type YearPickerResult struct {
+	Element *ui.Element
+	Changed bool
+}
+
+type yearKey struct{}
+
+// YearPicker lays out a decade's years; ◀ ▶ turn decades.
+func YearPicker(c *ui.Context, text string, year *int, o YearPickerOptions) YearPickerResult {
+	k := pixel.K(c)
+	col := ui.Column(c).Gap(k.D(2))
+	st := ui.Local(col, yearKey{}, func() paging { return paging{at: *year - *year%10, cur: *year % 10} })
+	res := YearPickerResult{Element: col}
+	col.Children(func() {
+		pager(c, fmt.Sprintf("%d–%d", st.at, st.at+9), 5*28, o.Disabled, func(d int) {
+			st.at += 10 * d
+			slog.Debug("8bit: year picker turned", "label", text, "decade", st.at)
+		})
+		shell, _, ps, picked := pixel.Pad(c, text, 5, 10, 28, cell, &st.cur, o.Disabled)
+		if picked >= 0 {
+			*year, res.Changed = st.at+picked, true
+		}
+		at, cur, chosen := st.at, st.cur, *year
+		shell.Draw(func(p *ui.Painter, r ui.Rect) {
+			g := k.Canvas(p, r)
+			for i := range 10 {
+				x, y := i%5*28, i/5*cell
+				if ps.Focus && i == cur {
+					g.Cursor(x, y, 28, cell)
+				}
+				if at+i == chosen {
+					g.Frame(x+1, y, 26, cell, pixel.Sunken, pixel.Well)
+				}
+				n := strconv.Itoa(at + i)
+				g.Text(x+(28-pixel.Measure(n))/2, y, n, pixel.Ink, 1)
+			}
+			g.Finish(ps)
+		})
+	})
+	if res.Changed {
+		slog.Debug("8bit: year picker", "label", text, "year", *year)
+	}
+	return res
+}