Deprecation of Existing std.io Readers and Writers in ziglang/zig

Although Reader and Writer are no longer generic, they are still transparent to optimization.

All of the interface functions have a concrete hot path operating on the buffer.

I have a lot more changes to upstream but it was taking too long to

Deprecates all existing std.io readers and writers in favor of the newly provided std.io.Reader and std.io.Writer which are non-generic and have the buffer above the vtable.