[SPARK-56956][SDP] Introduce AutoCDC Flow Dataclasses

[AnishMahto]

Approved AutoCDC SPIP: https://lists.apache.org/thread/j6sj9wo9odgdpgzlxtvhoy7szs0jplf7

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What changes were proposed in this pull request?

Introduce dataclass for unresolved AutoCDC flow (AutoCdcFlow) and resolved AutoCDC flow (AutoCdcMergeFlow). Add wiring to analyze an AutoCdcFlow to an AutoCdcMergeFlow.

A small refactor was additionally made on the UnresolvedFlow and ResolvedFlow class hierarchy.

Why are the changes needed?

Support AutoCDC flow registration and analysis. AutoCDC flow execution will be supported in a future PR. Previously, an UnresolvedFlow additionally always represented an untyped-flow; a flow where do not yet know its execution-type, i.e streaming, append-once, etc.

AutoCdcFlow is a specialized flow with support for only streaming flows, hence it represents a flow whose execution-type we know at construction. It is still unresolved at registration time, and needs to go through resolution to determine its position in the DAG and its input/output schemas.

Hence we introduce the intermediary child UntypedFlow for UnresolvedFlow, which all previous flows are classified as during registration. An AutoCdcFlow directly implements UnresolvedFlow (skipping `UntypedFlow in its inheritance chain) because it is not untyped.

Does this PR introduce any user-facing change?

No, the AutoCDC feature is not released anywhere yet.

How was this patch tested?

ConnectValidPipelineSuite and AutoCdcFlowSuite

Was this patch authored or co-authored using generative AI tooling?

Co-authored.

Generated-by: Claude-Opus-4.7-thinking-xhigh

[AnishMahto]

@szehon-ho

This is actually a fairly small change btw, 600 LOC is just tests. The only real logic added here is some validation on construction of an AutoCdcFlow.