Kick-start initial work on new cross-platform abstraction for
sockets. Adds a test for read timeouts and a test for creating
a non-blocking socket pair on Linux.
The new Socket abstraction is barebones and is made to support both
blocking and non-blocking abstractions, alongside different socket
protocols and domains.
Support for platform-dependant socket options that handles unsupported
platforms gracefully via. comptime checks is provided for the new Socket
abstraction.
This also marks the first out of many commits for introducing breaking
changes to the standard library in a separate `x` folder, which was
pre-approved by @andrewrk.
The intent for the new `x` package is to introduce new async, event loop,
networking, and operating system abstractions that would require breaking
the standard library significantly. By having the `x` package, code in the
standard library and compiler may then slowly be refactored to use the `x`
package. Once modules in the `x` package are stabilized, they can be moved
out of the `x` package, and a global 'grep' can be done to update import
paths that resolve to the stabilized module in the `x` package.
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