refactor: organize mapper tests by language and enforce typed fixtures

[steipete]

What Problem This Solves

A single 17,410-line mapper test file mixed 434 cases from unrelated languages and frameworks, making focused runs and maintenance difficult. Retry tests bypassed the real provider contract with any, and fixture directories remained after tests.

User Impact

No CLI behavior changes. Contributors can run the relevant language's tests directly; test fixtures clean up after each case, and TypeScript catches unused locals and parameters.

Why This Change Was Made

Move the existing mapper cases beside their language modules, retaining cross-mapper coverage in mapper.test.ts. Preserve every mapper test body and existing platform gate. Use complete typed provider fixtures and remove the two unused parameters found by the compiler before enabling its unused-code checks.

Evidence

• pnpm typecheck, pnpm lint, pnpm format:check, pnpm test, and pnpm build passed. The same 941 tests pass with the same 2 platform skips, now across 48 files.
• A post-format SHA256/multiset check confirms all 434 original mapper test bodies are byte-for-byte preserved.
• Isolated Codex autoreview completed all four evidence partitions: scoped-clean at P0–P2.
• Live package proof: pnpm pack:smoke built the tarball, installed it with production dependencies offline, and ran the installed CLI: packaged CLI smoke mapped 13 features (3 CUDA).
• Local full-suite duration was 43.78 s versus 29.18 s for the initial baseline on this shared machine; no speedup claim is made. The benefit is focused language runs and automatic fixture cleanup.

[clawsweeper]

🦞👀
ClawSweeper picked this up.

Pull request received. I will update this pull request when review starts.