made build.zig.

Has runner and tester for each day,
as well as a runner and tester for all the days.
Also has check step for zls.

src/days/template/lib.zig

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+const std = @import("std");

src/days/template/main.zig

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+const std = @import("std");
+const part1 = @import("part1.zig");
+const part2 = @import("part2.zig");
+const input = @embedFile("input.txt");
+
+pub fn main() !void {
+    const stdout = std.io.getStdErr().writer();
+    try stdout.print("Part1: {d}\n", .{part1.solve(input)});
+    try stdout.print("Part2: {d}\n", .{part2.solve(input)});
+}

src/days/template/part1.zig

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+const lib = @import("lib.zig");
+const std = @import("std");
+const utils = @import("utils");
+
+pub fn solve(comptime input: []const u8) i32 {
+    return input.len;
+}
+
+test "part1 sample" {
+    const input =
+        \\0
+    ;
+    try std.testing.expectEqual(solve(input), 1);
+}

src/days/template/part2.zig

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+const lib = @import("lib.zig");
+const std = @import("std");
+const utils = @import("utils");
+
+pub fn solve(comptime input: []const u8) i32 {
+    return input.len;
+}
+
+test "part2 sample" {
+    const input =
+        \\0
+    ;
+    try std.testing.expectEqual(solve(input), 1);
+}

src/utils/mod.zig

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+const std = @import("std");