tsb-perf-evolve: add Series.sortValues validity-oracle tests

[Copilot]

The tsb-perf-evolve AlphaEvolve program runs bun test tests/core/series.sortValues.test.ts as the correctness gate for every candidate, but that file did not exist — every candidate would fail validity on the first command.

Changes

• New file tests/core/series.sortValues.test.ts — 29 tests pinning the observable behaviour of Series.sortValues (anchored to src/core/series.ts:714 and pandas Series.sort_values where the spec is ambiguous):
  • Numeric-with-NaN across all four (ascending, naPosition) combinations, asserting both values and originating-row indices.
  • String dtype ascending/descending, with nulls in either position.
  • Mixed dtype: all-NaN stable order, no-NaN permutation, integer dtype preservation.
  • Empty Series: dtype and name preserved across every option combination.
  • Index-alignment invariant: output index at position i is the originating row's label, not the sorted index array (catches a common candidate bug).
  • Public signature: defaults check + a compile-time const r: Series<T> = s.sortValues() assertion so a signature change fails tsc --noEmit.
  • fast-check properties: length, permutation, monotonicity, idempotence-up-to-ties, label/value pairing, and stability (equal values keep input order).

Out of scope

Gaps #2–#5 in the issue (metric_direction frontmatter, releaseassets.githubusercontent.com firewall allowlist, loud-fail pandas install, scheduler starvation) live under .autoloop/programs/** and .github/workflows/autoloop.md, which AGENTS.md forbids this agent from modifying. They need a separate PR from autoloop maintainers before the program can be enabled end-to-end.