Fix/writergate

[Cohors1316]

Replaced all deprecated GenericWriters with std.Io.Writer.

zig build test passes.
zig build run-counter builds and runs.

As big as this is the only two real changes are the Writers in Terminal and wasm, and I would take a good look at those to see if I missed something. Note that I haven't created a way to verify the wasm version yet.

For reference:

var buffer: std.Io.Writer.Allocating = .init(allocator);
const writer = &buffer.writer;

is the closest replacement for

var buffer: std.array_list.Managed(u8) = .init(allocator);
const writer = buffer.writer();

for fixed writer

var buffer: [256]u8 = undefined;
var writer: std.Io.Writer = .fixed(&buffer);
const string = writer.buffered();