refactor(cache): split TushareCache endpoint specs and parsers (D2)

[StackOverFlow11]

Summary

Data Layer D2 — behavior-preserving internal refactor of
data/cache/tushare_cache.py. The 814-line facade is split so endpoint metadata
and raw parsers are reviewable in small files, while TushareCache stays the
public facade and every cache behavior is unchanged. This is not a cache
semantics change, not a performance/concurrency change, and not a data-quality
layer.

Changed files (6)

• new data/cache/tushare_specs.py (89 lines) — endpoint identifiers,
  ALL_ENDPOINTS, _GLOBAL_KEY, canonical-raw column sets + natural keys,
  FINA_FIELDS, _INDEX_WINDOW_DAYS, raw→canonical rename maps. Pure constants.
• new data/cache/tushare_parsers.py (216 lines) — the 10 raw endpoint
  parsers (_parse_daily/_adj/_suspend/_stk_limit/_index_weight/_namechange/ _stock_basic/_daily_basic/_fina/_index_member), moved verbatim.
• new data/cache/tushare_planning.py (22 lines) — the two leaf helpers
  _fields_hash / _compact.
• mod data/cache/tushare_cache.py — 814 → 596 lines; keeps the public
  TushareCache facade + read-through engine + FetchOne/FetchSnapshot;
  imports the moved pieces and re-exports the public names.
• mod docs/data/data_layer_contracts.md — factually records D2 implemented
  (D3–D6 still not).
• new tests/test_tushare_cache_modularization.py (5 tests) — narrow
  re-export-identity + module-boundary regression guard.

What moved vs what stayed in TushareCache

• Moved out: endpoint constants/specs, raw parsers, and the two leaf planning
  helpers.
• Stayed (unchanged): all public methods + signatures (daily_bars,
  adj_factor, suspend_d, stk_limit, daily_basic, fina_indicator,
  index_member_all, index_weight, namechange, stock_basic, stats,
  update_summary); dense per-symbol gap planning; index_weight 90-day paging;
  snapshot/dimension staleness; refresh_recent_days / recent_tail_overrides /
  not_ready_days / force_refresh; fetch_counts / written_counts /
  not_ready_counts; ok/empty/not_ready/failed coverage semantics; one-row-per-
  natural-key upsert.

Backward-compatible import guarantees

from data.cache.tushare_cache import TushareCache and the constant imports
(DAILY_BASIC, FINA_INDICATOR, INDEX_MEMBER_ALL, INDEX_WEIGHT, NAMECHANGE,
STK_LIMIT, STOCK_BASIC, SUSPEND_D, FINA_FIELDS, ALL_ENDPOINTS) all keep
working — the facade re-exports them (verified identity in the new test; exercised
by data/feed/tushare_fina.py and the existing cache tests).

Verification

• pytest tests/test_tushare_cache_market.py tests/test_tushare_cache_universe.py tests/test_tushare_cache_p4_3.py tests/test_data_updater.py tests/test_cache_config.py → all pass.
• pytest -p no:cacheprovider → 584 passed (579 prior + 5 new D2 tests).
• ruff check . → All checks passed!
• validate-config over all 17 config/*.yaml → all OK.
• run-phase0 --config config/example.yaml → ic_mean=0.9600, annual_return=0.8408 (no behavior drift).
• git diff --check main...HEAD → clean; merge-marker scan → 0.
• Secret scan over changed files → real .config.json token value 0 hits; no FAKE token in changed files.

Behavior-preserving internal refactor — no cache semantics change. Please
review before merge.