fix(motion): prevent callback leak on detaching VirtualClock

[Unnati1007]

Description

This PR fixes a permanent interval/callback leak inside the @termuijs/motion timer coalescing pool. When a VirtualClock is detached, active subscriptions are migrated back to the real timer pool. However, their returned unsub functions previously still pointed to the virtual clock's cleanup instead of the real timer pool. This PR tracks the active state of each subscription and correctly maps unsubscription back to the real pool when needed.

Related Issue

Closes #3733

Which package(s)?

@termuijs/motion

Type of Change

• 🐛 Bug fix (type:bug)
• ✨ Feature (type:feature)
• 📝 Docs (type:docs)
• 🧪 Tests (type:testing)
• ♻️ Refactor (type:refactor)
• 🎨 Design / UX (type:design)
• ♿ Accessibility (type:accessibility)
• ⚡ Performance (type:performance)
• 🔧 DevOps / CI (type:devops)
• 🔒 Security (type:security)

Checklist

• ⭐ You starred the repo. The needs-star check blocks your merge otherwise.
• Tests pass locally: bun vitest run
• Build passes: bun run build
• Typecheck passes: bun run typecheck
• You read CONTRIBUTING.md.
• Your PR title follows type: short description.
• Widget state mutators call markDirty() (if your change affects rendering).
• No new any types without an inline comment explaining why.
• No unrelated refactors bundled into this PR.

GSSoC 2026 Participation

• You are a GSSoC 2026 contributor.
• Your GSSoC profile: https://gssoc.girlscript.org/profile/Unnati1007

Screenshots / Recordings (UI changes)

N/A (This is a non-visual background backend timing pool leak fix).

Notes for the Reviewer

• Added a test case in timer-pool.test.ts verifying that calling unsub() after detaching a VirtualClock successfully unsubscribes the callback and cleans up the real timer intervals.

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📥 Commits

Reviewing files that changed from the base of the PR and between e4472c9 and ac8bb04.

📒 Files selected for processing (2)

• packages/motion/src/timer-pool.test.ts
• packages/motion/src/timer-pool.ts

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[Unnati1007]

@Karanjot786 Please review the PR, do lemme know if any changes needed and merge it under GSSoC'26

[Karanjot786]

Blocking — build-and-test fails on the PR own test (timer-pool.test.ts:120). Root cause: the migration loop (timer-pool.ts:96-103) never sets entry.active=false when moving a sub to the real pool, so the unsub closure takes the wrong branch and the callback stays registered — the exact leak claimed. Set active=false on migration.