[Iceberg CDC sink] Split late data and create commit windows

[ahmedabu98]

Adds the CDC sink's windowing stage:

• CommitWindows groups each destination's keyed changes into event-time commit windows and sorts them by primary key and sequence number via SortValues transform
• SplitLateData diverts every late pane to a replayable dead-letter output instead of letting it reach a window the committer may already have sealed.

Needs #39997 to get merged first.

Part of #39979

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