Use SCALE's `Compact`

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What is Compact

A "compact" or general integer encoding is sufficient for encoding large integers (up to 2**536) and is more efficient at encoding most values than the fixed-width version. (Though for single-byte values, the fixed-width integer is never worse.)

- https://docs.substrate.io/reference/scale-codec/

Here is an example of how it is already used for Status structure:

https://github.com/hyperledger/iroha/blob/b9f28442bf4225f1647901629a4baed3b122cc3c/telemetry/src/metrics.rs#L50-L71

Pros

• Iroha doesn't need to bother about different integer types in schema - just use universal compact.
• Space-efficiency: less load on block store and network communication

Cons

• Performance cost for encoding

TODO

Investigate the cost via profiling & benchmarks.