Fix generic async state-machine field tokens

[DavidObando]

Fixes #2749

Summary

• route hoisted closure captures through the canonical generic state-machine field-token resolver
• preserve non-generic, method-generic, combined, and nested-generic async emission
• add strict ILVerify/runtime coverage for awaits and hoisted type-parameter locals

Validation

• targeted issue matrix: 6/6 passed
• Core.Tests: 6,691 passed, 1 skipped
• Compiler.Tests: 3,407 passed
• rebuilt Oahu.Core: DownloadDecryptJob ILVerify findings reduced from 35 to 0

Deferred

Oahu.Core still reports two unrelated BookLibrary.AddPersons generic-interface findings; ILVerify also ends with its existing verifier IndexOutOfRangeException.