Create Pool for HTTP connections/SSL objects for reuse

[The-Voidwalker]

OpenSSLHttpHandler.SendAsync SSL objects should be pooled and reused where possible. This will also require making SSL methods thread safe.

[The-Voidwalker]

Currently migrating from use of raw SSL objects to IHttpConnection objects (technically done, since there was only ever support for HTTP/1.x, but 2 and 3 are not yet implemented). There will be separate ones for each major HTTP version (i.e. Http1Connection, Http2Connection, and Http3Connection). There will be a singular ConnectionPoolManager per client with separate ConnectionPools per HTTP version. Technically, HTTP/2 and HTTP/3 don't require a pool in the same way as HTTP/1 due to multiplexing, however the pool will still be used to manage the connection itself and access dedicated IO for each request.