refactor: let mls_init() take ClientId directly

[fewerner]

The FFI function already does this but we somehow didn't change the internal function.

What's new in this PR

---

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[github-actions]

Bencher Report

Branch	felix/refactor/mls-init-signature
Testbed	ubuntu-latest

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Benchmark	Latency	microseconds (µs)
Commit add f(group size)/cs1/mem/1002	📈 view plot ⚠️ NO THRESHOLD	15,087.00 µs
Commit add f(group size)/cs1/mem/2	📈 view plot ⚠️ NO THRESHOLD	662.73 µs
Commit add f(group size)/cs1/mem/202	📈 view plot ⚠️ NO THRESHOLD	3,731.50 µs
Commit add f(group size)/cs1/mem/402	📈 view plot ⚠️ NO THRESHOLD	6,678.20 µs
Commit add f(group size)/cs1/mem/602	📈 view plot ⚠️ NO THRESHOLD	10,182.00 µs
Commit add f(group size)/cs1/mem/802	📈 view plot ⚠️ NO THRESHOLD	12,609.00 µs
Commit add f(number clients)/cs1/mem/1002	📈 view plot ⚠️ NO THRESHOLD	987,000.00 µs
Commit add f(number clients)/cs1/mem/2	📈 view plot ⚠️ NO THRESHOLD	648.87 µs
Commit add f(number clients)/cs1/mem/202	📈 view plot ⚠️ NO THRESHOLD	78,454.00 µs
Commit add f(number clients)/cs1/mem/402	📈 view plot ⚠️ NO THRESHOLD	215,270.00 µs
Commit add f(number clients)/cs1/mem/602	📈 view plot ⚠️ NO THRESHOLD	423,650.00 µs
Commit add f(number clients)/cs1/mem/802	📈 view plot ⚠️ NO THRESHOLD	673,580.00 µs
Commit pending proposals f(group size)/cs1/mem/1002	📈 view plot ⚠️ NO THRESHOLD	113,220.00 µs
Commit pending proposals f(group size)/cs1/mem/2	📈 view plot ⚠️ NO THRESHOLD	22,413.00 µs
Commit pending proposals f(group size)/cs1/mem/202	📈 view plot ⚠️ NO THRESHOLD	40,865.00 µs
Commit pending proposals f(group size)/cs1/mem/402	📈 view plot ⚠️ NO THRESHOLD	56,142.00 µs
Commit pending proposals f(group size)/cs1/mem/602	📈 view plot ⚠️ NO THRESHOLD	79,770.00 µs
Commit pending proposals f(group size)/cs1/mem/802	📈 view plot ⚠️ NO THRESHOLD	90,843.00 µs
Commit pending proposals f(pending size)/cs1/mem/1	📈 view plot ⚠️ NO THRESHOLD	14,773.00 µs
Commit pending proposals f(pending size)/cs1/mem/101	📈 view plot ⚠️ NO THRESHOLD	112,050.00 µs
Commit pending proposals f(pending size)/cs1/mem/21	📈 view plot ⚠️ NO THRESHOLD	31,874.00 µs
Commit pending proposals f(pending size)/cs1/mem/41	📈 view plot ⚠️ NO THRESHOLD	53,158.00 µs
Commit pending proposals f(pending size)/cs1/mem/61	📈 view plot ⚠️ NO THRESHOLD	72,224.00 µs
Commit pending proposals f(pending size)/cs1/mem/81	📈 view plot ⚠️ NO THRESHOLD	91,976.00 µs
Commit remove f(group size)/cs1/mem/1002	📈 view plot ⚠️ NO THRESHOLD	9,522.20 µs
Commit remove f(group size)/cs1/mem/2	📈 view plot ⚠️ NO THRESHOLD	515.61 µs
Commit remove f(group size)/cs1/mem/202	📈 view plot ⚠️ NO THRESHOLD	1,877.60 µs
Commit remove f(group size)/cs1/mem/402	📈 view plot ⚠️ NO THRESHOLD	3,458.20 µs
Commit remove f(group size)/cs1/mem/602	📈 view plot ⚠️ NO THRESHOLD	5,133.60 µs
Commit remove f(group size)/cs1/mem/802	📈 view plot ⚠️ NO THRESHOLD	7,217.30 µs
Commit remove f(number clients)/cs1/mem/1002	📈 view plot ⚠️ NO THRESHOLD	12,463.00 µs
Commit remove f(number clients)/cs1/mem/2	📈 view plot ⚠️ NO THRESHOLD	132,330.00 µs
Commit remove f(number clients)/cs1/mem/202	📈 view plot ⚠️ NO THRESHOLD	108,370.00 µs
Commit remove f(number clients)/cs1/mem/402	📈 view plot ⚠️ NO THRESHOLD	84,985.00 µs
Commit remove f(number clients)/cs1/mem/602	📈 view plot ⚠️ NO THRESHOLD	60,416.00 µs
Commit remove f(number clients)/cs1/mem/802	📈 view plot ⚠️ NO THRESHOLD	36,121.00 µs
Commit update f(group size)/cs1/mem/1002	📈 view plot ⚠️ NO THRESHOLD	132,130.00 µs
Commit update f(group size)/cs1/mem/2	📈 view plot ⚠️ NO THRESHOLD	670.94 µs
Commit update f(group size)/cs1/mem/202	📈 view plot ⚠️ NO THRESHOLD	27,315.00 µs
Commit update f(group size)/cs1/mem/402	📈 view plot ⚠️ NO THRESHOLD	53,670.00 µs
Commit update f(group size)/cs1/mem/602	📈 view plot ⚠️ NO THRESHOLD	80,872.00 µs
Commit update f(group size)/cs1/mem/802	📈 view plot ⚠️ NO THRESHOLD	106,650.00 µs

🐰 View full continuous benchmarking report in Bencher

[istankovic]

@fewerner could you please rebase this?