Move paste encoding to the input package, test, optimize away one alloc

This moves our paste logic to `src/input` in preparation for exposing
this as part of libghostty-vt. This yields an immediate benefit of
unit tests for paste encoding. 

Additionally, we were able to remove one allocation on every unbracketed
paste path unless the input specifically contains a newline. Unlikely to
be noticable, but nice.

NOTE: This also includes one change in behavior: we no longer encode
`\r\n` and a single `\r`, but as a duplicate `\r\r`. This matches xterm
behavior and I don't think will result in any issues since duplicate
carriage returns should do nothing in well-behaved terminals.

src/input.zig

@@ -9,6 +9,7 @@ pub const command = @import("input/command.zig");
 pub const function_keys = @import("input/function_keys.zig");
 pub const keycodes = @import("input/keycodes.zig");
 pub const kitty = @import("input/kitty.zig");
+pub const paste = @import("input/paste.zig");
 
 pub const ctrlOrSuper = key.ctrlOrSuper;
 pub const Action = key.Action;