init

pub fn init(allocator: std.mem.Allocator, vtx_count: usize, idx_count: usize) std.mem.Allocator.Error!Builder {
        std.debug.assert(vtx_count >= 3);
        std.debug.assert(idx_count % 3 == 0);
        var vtx: @FieldType(Builder, "vertexes") = try .initCapacity(allocator, vtx_count);
        errdefer vtx.deinit(allocator);
        return .{
            .vertexes = vtx,
            .indices = try .initCapacity(allocator, idx_count),
        };
    }