Improve multi stop plan unit generation

[dirkschumacher]

Explored a bit to reduce some overhead when generating sequences for move generation. In addition this has the effect that we don't spawn go routines so deep in the search.

Below are two smaller benchmark tests. The full set I cannot yet run until #47 is fixed, but this already captures some of the benefits here as it's mostly about allocations.

name                                          old time/op    new time/op    delta
pkg:github.com/nextmv-io/nextroute goos:darwin goarch:arm64
SequenceGenerator3-8                            15.2µs ± 0%    13.6µs ± 0%  -10.39%
pkg:github.com/nextmv-io/nextroute/tests/golden goos:darwin goarch:arm64
Golden/testdata/precedence_pathologic.json-8    4.56ms ± 0%    2.29ms ± 0%  -49.73%

name                                          old alloc/op   new alloc/op   delta
pkg:github.com/nextmv-io/nextroute goos:darwin goarch:arm64
SequenceGenerator3-8                            6.38kB ± 0%    5.99kB ± 0%   -6.04%
pkg:github.com/nextmv-io/nextroute/tests/golden goos:darwin goarch:arm64
Golden/testdata/precedence_pathologic.json-8    9.74MB ± 0%    5.10MB ± 0%  -47.66%

name                                          old allocs/op  new allocs/op  delta
pkg:github.com/nextmv-io/nextroute goos:darwin goarch:arm64
SequenceGenerator3-8                              71.0 ± 0%      69.0 ± 0%   -2.82%
pkg:github.com/nextmv-io/nextroute/tests/golden goos:darwin goarch:arm64
Golden/testdata/precedence_pathologic.json-8     73.3k ± 0%     49.0k ± 0%  -33.26%

[merschformann]

In which state is this? 🤔

[dirkschumacher]

@merschformann I want to do some further benchmarking. I'll ping you all again once that is done

[dirkschumacher]

🤔 linter

[dirkschumacher]

Waiting on #47 to fix some benchmark tests