fix: prevent stale RSI cache in StochRSI

[stefan-jansen]

Summary

• compute RSI outside the cached StochRSI kernel
• keep the existing StochRSI function signatures and compiled stochastic calculation
• ensure an upgraded editable installation cannot retain older RSI behavior inside a transitive Numba cache

Root cause

Numba invalidated the cached RSI function after the missing-observation fix, but the separately cached StochRSI caller still embedded the prior compiled RSI implementation. A single missing close could therefore produce finite zero StochRSI values through the end of a series in a long-lived checkout.

Verification

• deterministic public compute_features(..., ["stochrsi"]) reproduction now passes
• focused missing-observation and indicator accuracy tests: 49 passed, 2 expected TA-Lib skips before all extras were installed
• complete all-extras suite: 3,913 passed, 1 skipped, 57 deselected
• uv run mkdocs build --strict
• uv build
• pre-commit run --all-files

Closes #35

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.