Performance of indexing PauliOperator with UnitRange

[jlapeyre]

This could be faster. But I haven't looked into it much.
The storage and indexing schemes for BitArray and PauliOperator are similar. But the performance for this operation is much better for the former.

julia> using QuantumClifford;

julia> rp = random_pauli(100);

julia> import Random;

julia> bv = Random.bitrand(100);

julia> @btime $rp[25:75];
  520.979 ns (28 allocations: 1.61 KiB)

julia> @btime $bv[25:75];
  19.052 ns (3 allocations: 96 bytes)

I'm not sure how much this comes up in practice. But I think it's worth noting it.

Versions

Julia v"1.11.2"

QuantumClifford v0.9.15