DESKTOP: CPU Scheduler, Latch, Spinlock and Running Jobs grids show when their snapshot was collected; latch and spinlock trends say where their data starts (part of #4966)

[erikdarlingdata]

Part of #4966.

Why

A newest-snapshot grid shows one collection, so it should name that collection. The viewer's other grids already do this with a last Collected column (bare time in the display zone, to the second, sorted on the stored DateTime), and the Lite twin uses the same form. The Latch and Spinlock trend charts draw a flat zero over an empty stretch, so they also need a data-start note.

What changes

• CPU Scheduler, Latch, Spinlock and Running Jobs grids each end in a Collected column bound to CollectionTimeLocal (display zone, to the second, in the viewer's current-culture display format) with SortMemberPath="CollectionTime".
• CPU Scheduler rows are now CpuSchedulerGridRow: the shared metric row plus the snapshot's CollectionTime on every row. It lives in the viewer, so the shared PerformanceMonitor.Common type that Lite also uses is unchanged.
• Latch and Spinlock snapshot SQL and records carry collection_time (a new last column and record field). RunningJobRow gains CollectionTimeLocal over its existing CollectionTime.
• Latch and Spinlock trends get a "Showing since" banner from ForCollectorTable("latch_stats") / ("spinlock_stats"). The load holds ViewerReadFanOut.Of(4) for the join, releases it, and runs the two probes under their own Of(2), outside the join, so a probe that throws costs only the note.

Limits

• The strips and the Configuration grids are in other PRs.
• No test builds the grids on a real STA thread; the column pins read the xaml and the row types.

Test plan

• RED (temporary mutation, reverted): binding the Spinlock Collected column to CollectionTime instead of CollectionTimeLocal failed ViewerSnapshotCollectedColumnTests 1 of 7 and ViewerGridTimeColumnSortMemberTests 3 of 95. GREEN after revert.
• New pins: each of the four grids' last column is Collected, bound to CollectionTimeLocal, sorted on CollectionTime; the CPU Scheduler load calls CpuSchedulerGridRow.Build; TheDisplayText_IsTheDisplayZonesWallTime_ToTheSecond pins the literal 2026-10-03 14:05:09 for a known UTC instant in UTC display mode, run under the invariant culture, for all four row types (it makes no claim about other cultures); every CPU Scheduler row carries the snapshot's time; the old label is gone from the xaml. ViewerGridTimeColumnSortMemberTests has four new rows. ViewerSnapshotTimeLiveTests is kept for the SQL time.
• Full Darling.Tests suite (once, final code): Total 21259, Failed 481, Skipped 244. 310 unique failing names; comm -23 against dev-local-failing-tests.txt is empty.
• --no-incremental build: 0 errors, 0 warnings.
• scrubcheck --diff exit 0; the public-text grep prints nothing.
• CI-only (STA/WPF): none of the new pins needs STA.

CHANGELOG

SECTION: Fixed
ENTRY: - Snapshot grids show when they were collected ([#5029]) - The desktop viewer's CPU Scheduler, Latch, Spinlock and Running Jobs grids now end in a Collected column that shows when the snapshot was collected, and the Latch and Spinlock trend charts say where their data starts when it begins after the chosen range.
REF: [#5029]: #5029