Some benchmarks need per-epoch state reset so every measured run does the same work.
Add `Bench::setup(...).run(...)` for untimed per-epoch setup.
The existing `run()` now delegates to `runImpl()` with an empty setup lambda, keeping the old API unchanged.
This vendors the upstream change from `martinus/nanobench`.
The upstream PR also adds tests that verify setup is excluded from timing and runs once before each epoch's iterations.
Those tests are not copied here because wiring them into `src/bench/nanobench.h` outside the benchmarking setup would be awkward.
The `Default is 1ms, so we are mostly relying ...` comment update matches current upstream `nanobench` master.
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Running a few benchmarks (which will be migrated in the next commit to use the new setup method) several times to showcase the spread:
./build/bin/bench_bitcoin -filter='^(BnBExhaustion|AddrManAddThenGood|DeserializeBlockTest|DeserializeAndCheckBlockTest|CheckBlockTest|LoadExternalBlockFile|FindByte|WalletCreatePlain|WalletCreateEncrypted|WalletLoadingDescriptors)$'
| ns/op | op/s | err% | total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
| 26,400,542.00 | 37.88 | 0.4% | 0.29 | `AddrManAddThenGood`
| 189,075.00 | 5,288.91 | 0.4% | 0.01 | `BnBExhaustion`
| ns/block | block/s | err% | total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
| 1,237,000.00 | 808.41 | 2.4% | 0.01 | `DeserializeAndCheckBlockTest`
| 893,333.00 | 1,119.40 | 0.6% | 0.01 | `DeserializeBlockTest`
| ns/op | op/s | err% | total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
| 31.62 | 31,622,370.70 | 0.2% | 0.01 | `FindByte`
| 5,506,875.00 | 181.59 | 1.4% | 0.06 | `LoadExternalBlockFile`
| 593,480,333.00 | 1.68 | 0.4% | 6.53 | `WalletCreateEncrypted`
| 174,305,167.00 | 5.74 | 0.7% | 1.93 | `WalletCreatePlain`
| 160,833,875.00 | 6.22 | 0.2% | 0.80 | `WalletLoadingDescriptors`
| ns/op | op/s | err% | total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
| 26,005,125.00 | 38.45 | 1.3% | 0.29 | `AddrManAddThenGood`
| 181,909.67 | 5,497.23 | 0.1% | 0.01 | `BnBExhaustion`
| ns/block | block/s | err% | total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
| 1,223,000.00 | 817.66 | 2.8% | 0.01 | `DeserializeAndCheckBlockTest`
| 892,917.00 | 1,119.92 | 0.7% | 0.01 | `DeserializeBlockTest`
| ns/op | op/s | err% | total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
| 31.58 | 31,660,608.70 | 0.5% | 0.01 | `FindByte`
| 5,612,750.00 | 178.17 | 1.1% | 0.06 | `LoadExternalBlockFile`
| 594,012,250.00 | 1.68 | 0.2% | 6.53 | `WalletCreateEncrypted`
| 174,668,334.00 | 5.73 | 0.8% | 1.92 | `WalletCreatePlain`
| 158,494,375.00 | 6.31 | 0.3% | 0.79 | `WalletLoadingDescriptors`
