#8 fix: make computeTrend time-independent via injectable now (#7)

fixes issue #7 — computeTrend gained an optional now param; trend tests now pass a fixed now so they are deterministic (full suite 146/146 green). Closes #7.

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Summary by cubic

Makes computeTrend deterministic by accepting an optional now parameter instead of calling new Date() internally, so trend calculations no longer depend on wall-clock time.

Bug Fixes

• computeTrend now takes an optional now argument; callers who don't pass it keep the previous behavior.
• Trend tests pass a fixed reference date, making the full suite deterministic and green (146/146).

Summary by CodeRabbit

• Bug Fixes

  • Trend calculations now use a consistent reference time, improving result stability across repeated evaluations.

• Tests

  • Trend behavior is now validated against a fixed reference date, making test outcomes more consistent and reliable.