feat(element/input): make accept event agnostic to u8 and u21 slices

There are now comptime checks in place an the corresponding triggered
event will be automatically converted to the correct type to support
simple ascii strings (`[]u8`) or utf-8 strings (`[]u21`).

examples/elements/input.zig

@@ -127,10 +127,7 @@ pub fn main() !void {
             .key => |key| if (key.eql(.{ .cp = 'c', .mod = .{ .ctrl = true } })) app.quit(),
             .accept => |input| {
                 defer allocator.free(input);
-                var string = try allocator.alloc(u8, input.len);
-                defer allocator.free(string);
-                for (0.., input) |i, char| string[i] = @intCast(char);
-                log.debug("Accepted input '{s}'", .{string});
+                log.debug("Accepted input '{s}'", .{input});
             },
             .err => |err| log.err("Received {s} with message: {s}", .{ @errorName(err.err), err.msg }),
             else => {},
@@ -165,5 +162,5 @@ const zterm = @import("zterm");
 const Color = zterm.Color;
 
 const App = zterm.App(union(enum) {
-    accept: []u21,
+    accept: []u8,
 });