Optimize RecordSetHeader.Add() avoid .Concat().ToArray(n)

[SergeiPavlov]

I see in dumps that EnumerableExtensions.ToArray() is a hotspot here

[botinko]

Imo linq concat could be better here, need to benchmark.

[SergeiPavlov]

Imo linq concat could be better here, need to benchmark.

Concat() and .ToArray() allocate at least 2 iterators
There is no way to avoid it
foreach() optimization can avoid them

And we cannot benchmark every change
That will slow down dev process 10 times

[botinko]

Iterators could be stack-allocated or even stripped from final code.

We achiving quality, not numbers of optimizations.

[botinko]

We don't need bechmarks every change, there a lot of places where optimization is obvious. Here it's questionable.
I think AI could create a bech for you in a seconds.

[botinko]

As discussed in Slack, it just slightly faster, then Columns.Columns.Concat(columns).ToArray(); (without passing n)