Keep the configure sheet alive between reads

[winebarrel]

Pressing Options can do nothing at all. Found while chasing the symptom in
NecoSaver, which grew from this
project's layout and inherited the bug.

Cause

configureSheet built a fresh ConfigureSheetController on every read and stored
it in the view's only slot:

override var configureSheet: NSWindow? {
    let controller = ConfigureSheetController { … }   // new every read
    sheetController = controller                       // drops the previous one
    return controller.window
}

The window's only owner was that slot, so the second read deallocated the window
handed out by the first. Two ways that bites:

• a host that reads the property twice — once to decide, once to present — is left
  presenting a deallocated window
• a host that replaces the ScreenSaverView between reading the property and
  presenting it loses the window along with the old view, which is what happens
  around display reconfiguration

Either way the sheet never appears, and no crash report is filed — the window is
simply gone by the time it is wanted. That is what makes it intermittent.

Separately, the window was left with isReleasedWhenClosed at its default of
true while ARC owned it through the controller: an over-release waiting for a
host that closes the sheet rather than ordering it out.

Fix

One controller, built on first use and kept. reload() re-reads the saved
settings each time the sheet is handed over, so reopening shows what is stored
rather than where the last visit was left. isReleasedWhenClosed turned off.

Verified

Driving the built bundle the way a host does, before and after:

                              before                    after
read #1                       NSWindow 0x…8000          NSWindow 0x…4000
read #2                       NSWindow 0x…d180          NSWindow 0x…4000
window from read #1           DEALLOCATED               alive
isReleasedWhenClosed          true                      false

Reuse does not leak edits — move a slider, cancel, reopen:

open 1: first slider = 12.0
open 1: moved to 25.0
same window reused: true
open 2: first slider = 12.0 (stored value — cancel was honoured)

Three present/dismiss rounds stay clean (attachedSheet back to nil each time).
Both schemes build and analyse; swiftlint --strict, swiftlint analyze --strict
and swiftformat --lint are clean.

What this does not prove is that the symptom is gone in practice — it is
intermittent, and the harness can only show that the mechanism behind it is. That
needs real use in System Settings.