update to new zig async io

[philipmv]

This is just as an experiment may be it should be in a separate branch. Unfortunately ssl connection is removed.

[karlseguin]

I'm not really following along...is TLS not currently working in Zig-dev, or just not ported in this PR yet?

[philipmv]

No, it's working. I just haven't looked into it and didn't port it. This PR is only useful if you are interested in using pg.zig with zig's new async io. It's very early, but someone may still be interested.

[lalinsky]

I was just looking at using pg.zig with my zio library, and though I could use this as the base, but it's very incomplete:

• still uses threads, especially for the reconnector
• timeouts need to be restored
• openssl will be a bigger issue, will either need to migrate to std.Io.Reader and use std.crypto.tls, or use openssl BIO APIs.

I'll give it a try to refactor the lib to use standard reader/writer, which would allow it to use std.crypto, that might be the easiest option.