refactor: run zigimports

closes: #38

src/buffer/Buffer.zig

@@ -6,7 +6,6 @@ const cwd = std.fs.cwd;
 
 const Self = @This();
 
-const default_leaf_capacity = 64;
 const max_imbalance = 7;
 pub const Root = *const Node;
 pub const unicode = @import("unicode.zig");

src/buffer/Selection.zig

@@ -1,5 +1,3 @@
-const std = @import("std");
-const Plane = @import("renderer").Plane;
 const Buffer = @import("Buffer.zig");
 const Cursor = @import("Cursor.zig");