refactor: remove MaybeArc [WPB-21755]

[fewerner]

What's new in this PR

This PR removes any MaybeArc implementation since we now always use Arc because we always use uniffi.

---

PR Submission Checklist for internal contributors

• The PR Title
  • conforms to the style of semantic commits messages¹ supported in Wire's Github Workflow²
  • contains a reference JIRA issue number like SQPIT-764
  • answers the question: If merged, this PR will: ... ³

1. https://sparkbox.com/foundry/semantic_commit_messages
2. https://github.com/wireapp/.github#usage
3. E.g. feat(conversation-list): Sort conversations by most emojis in the title #SQPIT-764.

[github-actions]

Bencher Report

Branch	felix/refactor/remove-maybe-arc
Testbed	ubuntu-latest

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Benchmark	Latency	microseconds (µs)
Commit add f(group size)/cs1/mem/1002	📈 view plot ⚠️ NO THRESHOLD	17,925.00 µs
Commit add f(group size)/cs1/mem/2	📈 view plot ⚠️ NO THRESHOLD	753.77 µs
Commit add f(group size)/cs1/mem/202	📈 view plot ⚠️ NO THRESHOLD	4,317.50 µs
Commit add f(group size)/cs1/mem/402	📈 view plot ⚠️ NO THRESHOLD	7,864.90 µs
Commit add f(group size)/cs1/mem/602	📈 view plot ⚠️ NO THRESHOLD	11,883.00 µs
Commit add f(group size)/cs1/mem/802	📈 view plot ⚠️ NO THRESHOLD	14,815.00 µs
Commit add f(number clients)/cs1/mem/1002	📈 view plot ⚠️ NO THRESHOLD	990,780.00 µs
Commit add f(number clients)/cs1/mem/2	📈 view plot ⚠️ NO THRESHOLD	712.06 µs
Commit add f(number clients)/cs1/mem/202	📈 view plot ⚠️ NO THRESHOLD	78,734.00 µs
Commit add f(number clients)/cs1/mem/402	📈 view plot ⚠️ NO THRESHOLD	214,640.00 µs
Commit add f(number clients)/cs1/mem/602	📈 view plot ⚠️ NO THRESHOLD	420,230.00 µs
Commit add f(number clients)/cs1/mem/802	📈 view plot ⚠️ NO THRESHOLD	667,560.00 µs
Commit pending proposals f(group size)/cs1/mem/1002	📈 view plot ⚠️ NO THRESHOLD	115,390.00 µs
Commit pending proposals f(group size)/cs1/mem/2	📈 view plot ⚠️ NO THRESHOLD	22,872.00 µs
Commit pending proposals f(group size)/cs1/mem/202	📈 view plot ⚠️ NO THRESHOLD	41,468.00 µs
Commit pending proposals f(group size)/cs1/mem/402	📈 view plot ⚠️ NO THRESHOLD	57,515.00 µs
Commit pending proposals f(group size)/cs1/mem/602	📈 view plot ⚠️ NO THRESHOLD	76,589.00 µs
Commit pending proposals f(group size)/cs1/mem/802	📈 view plot ⚠️ NO THRESHOLD	92,681.00 µs
Commit pending proposals f(pending size)/cs1/mem/1	📈 view plot ⚠️ NO THRESHOLD	17,808.00 µs
Commit pending proposals f(pending size)/cs1/mem/101	📈 view plot ⚠️ NO THRESHOLD	114,990.00 µs
Commit pending proposals f(pending size)/cs1/mem/21	📈 view plot ⚠️ NO THRESHOLD	34,891.00 µs
Commit pending proposals f(pending size)/cs1/mem/41	📈 view plot ⚠️ NO THRESHOLD	55,962.00 µs
Commit pending proposals f(pending size)/cs1/mem/61	📈 view plot ⚠️ NO THRESHOLD	74,660.00 µs
Commit pending proposals f(pending size)/cs1/mem/81	📈 view plot ⚠️ NO THRESHOLD	94,401.00 µs
Commit remove f(group size)/cs1/mem/1002	📈 view plot ⚠️ NO THRESHOLD	11,280.00 µs
Commit remove f(group size)/cs1/mem/2	📈 view plot ⚠️ NO THRESHOLD	576.54 µs
Commit remove f(group size)/cs1/mem/202	📈 view plot ⚠️ NO THRESHOLD	2,249.10 µs
Commit remove f(group size)/cs1/mem/402	📈 view plot ⚠️ NO THRESHOLD	4,128.20 µs
Commit remove f(group size)/cs1/mem/602	📈 view plot ⚠️ NO THRESHOLD	6,210.40 µs
Commit remove f(group size)/cs1/mem/802	📈 view plot ⚠️ NO THRESHOLD	8,140.80 µs
Commit remove f(number clients)/cs1/mem/1002	📈 view plot ⚠️ NO THRESHOLD	14,164.00 µs
Commit remove f(number clients)/cs1/mem/2	📈 view plot ⚠️ NO THRESHOLD	135,200.00 µs
Commit remove f(number clients)/cs1/mem/202	📈 view plot ⚠️ NO THRESHOLD	110,960.00 µs
Commit remove f(number clients)/cs1/mem/402	📈 view plot ⚠️ NO THRESHOLD	86,630.00 µs
Commit remove f(number clients)/cs1/mem/602	📈 view plot ⚠️ NO THRESHOLD	62,285.00 µs
Commit remove f(number clients)/cs1/mem/802	📈 view plot ⚠️ NO THRESHOLD	38,575.00 µs
Commit update f(group size)/cs1/mem/1002	📈 view plot ⚠️ NO THRESHOLD	135,150.00 µs
Commit update f(group size)/cs1/mem/2	📈 view plot ⚠️ NO THRESHOLD	748.31 µs
Commit update f(group size)/cs1/mem/202	📈 view plot ⚠️ NO THRESHOLD	28,010.00 µs
Commit update f(group size)/cs1/mem/402	📈 view plot ⚠️ NO THRESHOLD	55,058.00 µs
Commit update f(group size)/cs1/mem/602	📈 view plot ⚠️ NO THRESHOLD	83,154.00 µs
Commit update f(group size)/cs1/mem/802	📈 view plot ⚠️ NO THRESHOLD	108,960.00 µs

🐰 View full continuous benchmarking report in Bencher

[coriolinus]

I really don't like the prevalence of Arc::unwrap_or_clone, given how unnecessary it is. And the changes to Cargo.toml need reverting.

Even so, this is great work, and I'm looking forward to approving it soon.