perf: HttpConnection write bytes directly into the buffer

[campersau]

Benchmark on net10.0

Method	Mean	Error	StdDev	Gen0	Allocated
PR	710.7 ns	14.01 ns	20.53 ns	0.0467	616 B
main	786.3 ns	15.67 ns	23.45 ns	0.1125	1480 B

[HofmeisterAn]

I think the many preprocessor directives make the code hard to read. I propose using proper abstraction (a base class) and separate implementations for the underlying buffer (ArrayBufferWriter and MemoryStream) that handle writing to the buffer. Then we can use a single preprocessor directive to include the class entirely, like we're doing here. Then we don't need if-else in HttpConnection.

[campersau]

Do you mean something like this dd4d234?

[HofmeisterAn]

Do you mean something like this dd4d234?

See my recent changes, I was thinking of something like this. WDYT? I'll take another look tomorrow, but I think it's easier to read now.

[campersau]

Ah ok. Yes, looks good to me!