Optimize stacktrace from 7.36kB to 2.30kB and speed too

[YaroslavPodorvanov]

go test ./... -run=$^ -bench=Benchmark -benchmem -count=10 > old.txt
go test ./... -run=$^ -bench=Benchmark -benchmem -count=10 > new.txt
benchstat old.txt new.txt

name              old time/op    new time/op    delta
ProcessEvent-12     1.50µs ±14%    1.56µs ±22%     ~     (p=0.684 n=10+10)
NewStacktrace-12    8.24µs ±25%    4.34µs ±14%  -47.30%  (p=0.000 n=10+10)

name              old alloc/op   new alloc/op   delta
ProcessEvent-12       946B ± 0%      939B ± 0%   -0.73%  (p=0.000 n=10+7)
NewStacktrace-12    7.36kB ± 0%    2.30kB ± 0%  -68.70%  (p=0.000 n=10+10)

name              old allocs/op  new allocs/op  delta
ProcessEvent-12       4.00 ± 0%      4.00 ± 0%     ~     (all equal)
NewStacktrace-12      15.0 ± 0%       4.0 ± 0%  -73.33%  (p=0.000 n=10+10)

[YaroslavPodorvanov]

this is main optimization of NewStacktrace because append faster that prepend and use less memory

[YaroslavPodorvanov]

@kamilogorek can you review please?

[YaroslavPodorvanov]

@bruno-garcia can you review code?

[kamilogorek]

@YaroslavPodorvanov I'll catch up on everything this week. We had company-wide hackweek, so everyone was slow to review external contributions :)

[kamilogorek]

Thanks 🙇