refactor(fuzz)!: remove the @deprecated Proposer<S> alias

[drewstone]

What

Deletes the @deprecated export type Proposer<S> = MutationProposer<S> back-compat alias from src/fuzz/types.ts and its re-export from the ./fuzz barrel (src/fuzz/index.ts). MutationProposer<S> is now the only name for the fuzz scenario-generator function type.

PR #278 renamed the fuzz Proposer<S> to MutationProposer<S> (to disambiguate from the optimization SurfaceProposer) but kept the alias for back-compat. The repo's house rule forbids compat shims on greenfield/substrate surfaces, so this removes it head-on — no fallback.

The fuzz module itself stays — it is load-bearing across the fleet; only the deprecated type alias goes.

Scope

• src/fuzz/types.ts — deletes the 3-line @deprecated alias.
• src/fuzz/index.ts — drops Proposer from the ./fuzz type re-export.
• Version trio bumped together 0.97.0 → 0.98.0 (npm + PyPI lock-step): package.json, clients/python/pyproject.toml, clients/python/src/agent_eval_rpc/__init__.py. Removing a published export is breaking on a 0.x line, so a minor bump.

SurfaceProposer / SelfPlayProposer / OptimizationProposer are different types and are untouched.

Verification

• pnpm run typecheck — clean.
• pnpm run build — clean; built dist/fuzz.d.ts export list no longer contains a bare Proposer (only type MutationProposer and the mutationProposer factory).
• pnpm test — 247 files, 2533 passed, 2 skipped, 0 failed.
• pnpm run lint — no errors (pre-existing warnings only, unrelated files).

[tangletools]

✅ Auto-approved PR — 889fe9fd

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_{tangletools · auto-approval · reason: blanket_auto_approve · 2026-06-22T23:09:04Z}