Add fractional Duration total accessors

[brickfrog]

Closes tempo-z7j.3. Adds Duration::as_seconds_f64, Duration::as_minutes_f64, and Duration::as_hours_f64 by converting total nanoseconds to Double and dividing by Double unit literals. Includes exact public API tests for fractional, negative, and zero cases.

Verification

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• moon fmt --check
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Finished. moon: no work to do

• moon test --target wasm-gc
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Total tests: 285, passed: 285, failed: 0.

• moon test --target js
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Total tests: 285, passed: 285, failed: 0.

• moon test --target native
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Total tests: 285, passed: 285, failed: 0.

[brickfrog]

Choir: GitHub Actions rollup reports all checks successful on the latest head — re-check review/merge policy on GitHub (not an approval or merge signal by itself).

[Copilot]

Pull request overview

This PR extends Duration’s accessor API with fractional “total” conversions, allowing callers to retrieve the full duration in seconds/minutes/hours as Double without truncation, and adds targeted tests to validate the new behavior.

Changes:

• Add Duration::as_seconds_f64, Duration::as_minutes_f64, and Duration::as_hours_f64 accessors.
• Document precision limits inherent to Double for large magnitudes.
• Add tests covering fractional, negative, and zero durations for the new accessors.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/tempo.mbt	Adds new Double-returning total accessor APIs for seconds/minutes/hours.
src/tempo_test.mbt	Adds unit tests validating the new fractional accessor behavior.
src/pkg.generated.mbti	Exposes the new public APIs in the generated interface.

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[brickfrog]

Choir: comment-only review received — routed to main.ergo-task-add-fractional-total-1780418501483-596086 (leaf pane).

[brickfrog]

Choir: GitHub Copilot issue-thread comment observed on PR — parent notified with updated gate snapshot (not merge approval).

[brickfrog]

Choir: fixes pushed by main.ergo-task-add-fractional-total-1780418501483-596086 — resolving threads and checking gates (not merged yet).

[brickfrog]

Choir: GitHub Actions rollup reports all checks successful on the latest head — re-check review/merge policy on GitHub (not an approval or merge signal by itself).