[DS][13/n] Convert SchedulingContext to DagsterModel

[OwenKephart]

Summary & Motivation

Makes a couple changes to allow using the DagsterModel class instead of dataclass

How I Tested These Changes

[OwenKephart]

• #21641 : 2 dependent PRs (#21670 , #21671 )
• #21640
• #21648
• #21615
• #21613
• #21612
• #21573
• #21546
• #21545
• #21541
• #21540
• #21539
• #21538
• #21537
• #21536
• #21535
• #21521 👈
• #21520
• #21511 : 1 other dependent PR (#21512 )
• #21510
• #21508
• #21507
• #21505
• #21504
• #21503
• #21502
• #21501
• #21500
• #21499
• master

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[OwenKephart]

@schrockn I narrow the type at the top of the stack (25/n)

[OwenKephart]

Merge activity

• May 3, 5:31 PM EDT: @OwenKephart started a stack merge that includes this pull request via Graphite.
• May 3, 5:57 PM EDT: Graphite rebased this pull request as part of a merge.
• May 3, 5:58 PM EDT: @OwenKephart merged this pull request with Graphite.