[Feature] Reduction-aware inlining (ADR 0020 stage 3: move the inline decision into `quote`)

[katsujukou]

Summary

Complete ADR 0020 stage 3: make inlining decisions reduction-aware by driving them from
the NbE quote, instead of a pre-selected candidate set.

Status / evidence

• ADR 0020: stages 1–2 done — the NbE core (Semantics's Sem/eval/quote) is the
  default reducer (DictElim.useNbE = true) and reproduces the existing
  Inline.inlineCandidates set. Stage 3 (reduction-aware decision in quote) is not
  started.

Direction

Decide inlining during quotation based on whether it unlocks further reduction, rather than
the heuristic candidate set.

[katsujukou]

With PR #43 merged, reduction-aware inliner is now working. Close.