vlib: io: Buffered IO, x.net -> net

[emily33901]

The spiritual successor to #6299 This PR Adds buffered io and general purpose interfaces for reading, writing, and a simple buffered reader struct that can be fleshed out more when needed.

Also moves x.net -> net and fixes smtp, ftp, http, x.websocket, and everything else.

read_into is renamed to read to be inline with the Reader interface that itself uses the name from the Go reader interface. Since io.read_all() can now be used to read any bytes that a reader has I feel that this is fine

I think just the vweb test is busted but thats because it does some silly tcpconn opening stuff.

[esquerbatua]

Great job!

[medvednikov]

>> webserver: started on http://127.0.0.1:12380/ , with maximum runtime of 5000 milliseconds.

/home/runner/work/v/v/vlib/vweb/tests/vweb_test.v:53: failed assert in function assert_common_headers
Source  : `received.starts_with('HTTP/1.1 200 OK\\r\\n')`

/home/runner/work/v/v/vlib/vweb/tests/vweb_test.v:74: failed assert in function test_a_simple_tcp_client_simple_route
Source  : `err == ''`
	 left value: net: socket error: 88 <= `err`
	right value:  <= `''`

/home/runner/work/v/v/vlib/vweb/tests/vweb_test.v:87: failed assert in function test_a_simple_tcp_client_html_page
Source  : `err == ''`
	 left value: net: socket error: 32 <= `err`
	right value:  <= `''`
V panic: net: socket error: 111```

[medvednikov]

Great work @emily33901 !

Looking forward to merging this.