Make example binaries proper cargo examples (#7019)

Should not be built by default with `cargo build`
Instead are compiled with `cargo test` to avoid bitrot
Run with `cargo run -p ... --example ...`

crates/nu-term-grid/examples/grid.rs

@@ -0,0 +1,30 @@
+use nu_term_grid::grid::{Alignment, Cell, Direction, Filling, Grid, GridOptions};
+
+// This produces:
+//
+//  1 |  128 |   16384 |   2097152 |   268435456 |   34359738368 |   4398046511104
+//  2 |  256 |   32768 |   4194304 |   536870912 |   68719476736 |   8796093022208
+//  4 |  512 |   65536 |   8388608 |  1073741824 |  137438953472 |  17592186044416
+//  8 | 1024 |  131072 |  16777216 |  2147483648 |  274877906944 |  35184372088832
+// 16 | 2048 |  262144 |  33554432 |  4294967296 |  549755813888 |  70368744177664
+// 32 | 4096 |  524288 |  67108864 |  8589934592 | 1099511627776 | 140737488355328
+// 64 | 8192 | 1048576 | 134217728 | 17179869184 | 2199023255552 |
+
+fn main() {
+    let mut grid = Grid::new(GridOptions {
+        direction: Direction::TopToBottom,
+        filling: Filling::Text(" | ".into()),
+    });
+
+    for i in 0..48 {
+        let mut cell = Cell::from(format!("{}", 2_isize.pow(i)));
+        cell.alignment = Alignment::Right;
+        grid.add(cell)
+    }
+
+    if let Some(grid_display) = grid.fit_into_width(80) {
+        println!("{}", grid_display);
+    } else {
+        println!("Couldn't fit grid into 80 columns!");
+    }
+}