logging: implement WAL for net writer

[mohammed90]

After wrestling with it for ~1.5 years, I caved and used Cody. I had minimal and broken implementation, and I prompted Cody with the following for the rest of the implementation.

The NetWriter logger writes log lines to the network synchronously, meaning it'll block the HTTP request handling if the network is slow. This is not ideal. The NetWriter should write to a WAL (Write-Ahead-Log) that is asynchrounously flushed to the network. When the server is stopping, it should flush the full WAL. When the server starts and WAL is present, it should append to it and try to flush it. The code currently is the start of an attempt to implement this but is incomplete and likely incorrect. Implement the requirement properly.

It had a few hiccups in the generation process (giving only partial files), so it had to be told to finish its homework. Then I asked it to generate the tests with this prompt:

can you add a test for the WAL implementation? The test should be in a new file named netwriter_test.go

Two of the test functions fail. Cody keeps trying to fix the tests instead of fixing the code. I also see unused struct field is introduced. Manual polishing work is WIP. Support is welcome.

Closes #5697

[mholt]

Wow 💦 Cool -- thanks for iterating on this. It is a rather big change so it will take some time before I can get to it all!