Address comments from @ifreund and @MasterQ32 to address unsafeness and
ergonomics of the `Address` API.
Rename the `TCP` namespace to `tcp` as it does not contain any
top-level fields.
Fix missing reference to `sockaddr` which was identified by @kprotty in
os/bits/linux/arm64.zig.
The `Socket` abstraction was refactored to only comprise of methods that
can be generically used/applied to all socket domains and protocols.
A more comprehensive IPv4/IPv6 module derived from @LemonBoy's earlier
work was implemented under `std.x.os.IPv4` and `std.x.os.IPv6`. Using
this module, one can then combine them together into a union for example
in order to optimize memory usage when dealing with socket addresses.
A `TCP.Client` and `TCP.Listener` abstraction is introduced that is one
layer over the `Socket` abstraction, which isolates methods that can
only be applied to a "client socket" and a "listening socket". All prior
tests from the `Socket` abstraction, which all previously operated
assuming the socket is operating via. TCP/IP, were moved. All TCP socket
options were also moved into the `TCP.Client` and `TCP.Listener`
abstractions respectively away from the `Socket` abstraction.
Some additional socket options from @LemonBoy's prior PR for Darwin were
also moved in (i.e. SIGNOPIPE).
