fix(vector): normalize captured Chaikin helper

[vntrevx]

Intent

Unblock the v1.6.0 installed-wheel release gate after build run 31736493335 found the same Full Native source-compiler blocker on Linux, Windows, and macOS.

Change

• Normalize explicit np.zeros_like(..., dtype=np.float64) into the existing generic array IR.
• Recognize the X7 Chaikin helper whose numerator and denominator both use the source-defined NaN-tolerant rolling sum, and lower it to the existing generic Rust Chaikin kernel.
• Add focused compiler regressions and document the release behavior.
• No strategy version, pair, timerange, SHA, or expected-result runtime branch.

Validation

• uv run pytest -q tests/test_indicator_program.py tests/test_full_vector_runtime.py (38 passed)
• uv run ruff check .
• uv run basedpyright --level error python/nfi_backtest_engine
• Release-candidate Spot fixture --level full: trade surface and state exact
• Release-candidate Futures fixture --level full: trade surface and state exact

The earlier failed build is retained as diagnostic evidence; the release workflow will only be dispatched again after this PR's Required CI and the resulting same-commit main CI pass.

[chatgpt-codex-connector]

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