core: miner: reduce allocations in block building

[MariusVanDerWijden]

I recently went on a longer flight and started profiling the geth block production pipeline.
This PR contains a bunch of individual fixes split into separate commits.
I can drop some if necessary.

Benchmarking is not super easy, the benchmark I wrote is a bit non-deterministic.
I will try to write a better benchmark later

goos: linux
goarch: amd64
pkg: github.com/ethereum/go-ethereum/miner
cpu: Intel(R) Core(TM) Ultra 7 155U
                │ /tmp/old.txt │          /tmp/new.txt          │
                │    sec/op    │   sec/op     vs base           │
BuildPayload-14    141.5µ ± 3%   146.0µ ± 6%  ~ (p=0.346 n=200)

                │ /tmp/old.txt │             /tmp/new.txt             │
                │     B/op     │     B/op      vs base                │
BuildPayload-14   188.2Ki ± 4%   177.4Ki ± 4%  -5.71% (p=0.018 n=200)

                │ /tmp/old.txt │            /tmp/new.txt             │
                │  allocs/op   │  allocs/op   vs base                │
BuildPayload-14    2.703k ± 4%   2.453k ± 5%  -9.25% (p=0.000 n=200)