Fixes#1656
When called as part of window restoration AppKit has a lock, so
NSAppearance changes need to be called async.
See deadlock:
```
Thread 1 Queue : com.apple.main-thread (serial)
0 0x000000018fd63fac in __ulock_wait ()
1 0x00000001069bf720 in _dlock_wait ()
2 0x00000001069bfaec in _dispatch_group_wait_slow ()
3 0x0000000106b5f5c4 in interposed_dispatch_group_wait ()
4 0x00000001937fb1f0 in NSCGSTransactionRunPreCommitActions_ ()
5 0x00000001938f1230 in -[_NSCGSTransaction synchronize] ()
6 0x00000001938f11ac in NSCGSTransactionSynchronize ()
7 0x000000019382ad30 in +[NSCGSWindow(NSCGSSpace) isAnyWindowOnAVisibleSpace:] ()
8 0x000000019382a968 in -[NSWindow _isInSomeVisibleSpace] ()
9 0x000000019382a8e4 in -[NSWindow isOnActiveSpace] ()
10 0x0000000193db8d98 in -[NSApplication(NSApplicationAppearance_Internal) _invalidateWindowAppearances] ()
11 0x00000001938f44d4 in -[NSApplication(NSAppearanceCustomization) setAppearance:] ()
12 0x0000000102c48050 in AppDelegate.syncAppearance() at /Users/mitchellh/code/go/src/github.com/mitchellh/ghostty/macos/Sources/App/macOS/AppDelegate.swift:412
13 0x0000000102c47840 in AppDelegate.configDidReload(_:) at /Users/mitchellh/code/go/src/github.com/mitchellh/ghostty/macos/Sources/App/macOS/AppDelegate.swift:380
14 0x0000000102c43c7c in AppDelegate.applicationDidFinishLaunching(_:) at /Users/mitchellh/code/go/src/github.com/mitchellh/ghostty/macos/Sources/App/macOS/AppDelegate.swift:110
```
Corrected logic for detecting if the current row is the end of the
selection. Previous logic was faulty because when I calculated the
current page y incorrectly, not realizing that it was already
available as `y`.
More readable (smaller) output when failing, catches more edge cases.
At the time of this commit, this test is failing. Changed primarily to
address the edge case that was missed before.
