perf(buffer): simplify Buffer::filled with macro (#1036)

The `vec![]` macro is highly optimized by the Rust team and shorter.
Don't do it manually.

This change is mainly cleaner code. The only production code that uses
this is `Terminal::with_options` and `Terminal::insert_before` so it's
not performance relevant on every render.

benches/block.rs

@@ -1,8 +1,7 @@
-use criterion::{criterion_group, criterion_main, BatchSize, Bencher, BenchmarkId, Criterion};
+use criterion::{criterion_group, criterion_main, BatchSize, Bencher, Criterion};
 use ratatui::{
     buffer::Buffer,
-    layout::Rect,
+    layout::{Alignment, Rect},
-    prelude::Alignment,
     widgets::{
         block::{Position, Title},
         Block, Borders, Padding, Widget,
@@ -13,23 +12,23 @@ use ratatui::{
 fn block(c: &mut Criterion) {
     let mut group = c.benchmark_group("block");
 
-    for buffer_size in [
+    for (width, height) in [
-        Rect::new(0, 0, 100, 50),  // vertically split screen
+        (100, 50),  // vertically split screen
-        Rect::new(0, 0, 200, 50),  // 1080p fullscreen with medium font
+        (200, 50),  // 1080p fullscreen with medium font
-        Rect::new(0, 0, 256, 256), // Max sized area
+        (256, 256), // Max sized area
     ] {
-        let buffer_area = buffer_size.area();
+        let buffer_size = Rect::new(0, 0, width, height);
 
         // Render an empty block
         group.bench_with_input(
-            BenchmarkId::new("render_empty", buffer_area),
+            format!("render_empty/{width}x{height}"),
             &Block::new(),
             |b, block| render(b, block, buffer_size),
         );
 
         // Render with all features
         group.bench_with_input(
-            BenchmarkId::new("render_all_feature", buffer_area),
+            format!("render_all_feature/{width}x{height}"),
             &Block::new()
                 .borders(Borders::ALL)
                 .title("test title")

src/buffer/buffer.rs

@@ -55,22 +55,21 @@ pub struct Buffer {
 
 impl Buffer {
     /// Returns a Buffer with all cells set to the default one
+    #[must_use]
     pub fn empty(area: Rect) -> Self {
-        let cell = Cell::default();
+        Self::filled(area, &Cell::default())
-        Self::filled(area, &cell)
     }
 
     /// Returns a Buffer with all cells initialized with the attributes of the given Cell
+    #[must_use]
     pub fn filled(area: Rect, cell: &Cell) -> Self {
         let size = area.area() as usize;
-        let mut content = Vec::with_capacity(size);
+        let content = vec![cell.clone(); size];
-        for _ in 0..size {
-            content.push(cell.clone());
-        }
         Self { area, content }
     }
 
     /// Returns a Buffer containing the given lines
+    #[must_use]
     pub fn with_lines<'a, Iter>(lines: Iter) -> Self
     where
         Iter: IntoIterator,