Port v1.23.0-rc16 scheduler workflow into current package

[hehaifengcn]

Replace the scheduler workflow implementation with the v1.23.0-rc16 logic
while reusing the current package's compatible siblings (spec.go, buffer.go,
calendar.go, activities.go, fx.go, query.go).

Adaptations to the rc16 workflow:

• searchattribute.* -> sadefs.* (constants moved between 1.23 and 1.31)
• NewCompiledSpec -> specBuilder.NewCompiledSpec; getNextTime/getNextTimeResult
  -> GetNextTime/GetNextTimeResult; processBuffer -> ProcessBuffer with exported
  result fields
• defaultLocalActivityOptions var -> func() to match current activities.go

Preserved exports so the rest of the server still builds:

• schedulerWorkflowWithSpecBuilder (4-arg) and GetListInfoFromStartArgs (3-arg)
• SignalNameMigrateToChasm (ignored by v1.23 logic) and CurrentTweakablePolicies
  with a kept-for-compat SpecFieldLengthLimit field

Full production build (go build ./...) passes.

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com

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How did you test it?

• built
• run locally and tested manually
• covered by existing tests
• added new unit test(s)
• added new functional test(s)

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