Use ratatui's line_count for exact wrapped-row count

v0.1.1's max_scroll used ceil(display_width / width) per Line to
estimate wrapped rows, but ratatui's WordWrapper can exceed that
ceiling: with trim: false, a short trailing word forces the next
word to the next row while leaving whitespace on the previous row,
producing more rows than a naive division.

Concrete case: "one two three four five six seven eight" at W=10
word-wraps to 5 rows, but ceil(39/10) = 4. Our estimate was one row
short — exactly the bug the user saw after v0.1.1.

Defer to ratatui by enabling its unstable-rendered-line-info feature
and calling Paragraph::line_count(width), which runs the same
WordWrapper the renderer uses. Counts are authoritative.

Add a regression test that captures the word-boundary case ratatui
exceeds the ceiling on; correct the previous "hello world" at W=4
assertion to the 4 rows ratatui actually produces.

Author: skibitsky

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "mdview"
-version = "0.1.1"
+version = "0.1.2"
 edition = "2024"
 description = "A terminal markdown viewer"
 license = "MIT"
@@ -13,6 +13,6 @@ ansi-to-tui = "7"
 crossterm = { version = "0.28", features = ["event-stream"] }
 notify = "7"
 pulldown-cmark = { version = "0.12", default-features = false, features = ["simd"] }
-ratatui = "0.29"
+ratatui = { version = "0.29", features = ["unstable-rendered-line-info"] }
 syntect = { version = "5", default-features = false, features = ["default-syntaxes", "default-themes", "regex-fancy"] }
 unicode-width = "0.2"

Cargo.toml

@@ -1,5 +1,5 @@
 use ratatui::text::Text;
-use unicode_width::UnicodeWidthStr;
+use ratatui::widgets::{Paragraph, Wrap};
 
 pub struct App {
     pub text: Text<'static>,
@@ -12,18 +12,9 @@ pub fn wrapped_row_count(text: &Text<'_>, width: u16) -> u32 {
     if width == 0 {
         return text.lines.len() as u32;
     }
-    let w = width as u32;
-    text.lines
-        .iter()
-        .map(|line| {
-            let display: u32 = line
-                .spans
-                .iter()
-                .map(|s| UnicodeWidthStr::width(s.content.as_ref()) as u32)
-                .sum();
-            if display == 0 { 1 } else { display.div_ceil(w) }
-        })
-        .sum()
+    Paragraph::new(text.clone())
+        .wrap(Wrap { trim: false })
+        .line_count(width) as u32
 }
 
 impl App {
@@ -95,7 +86,15 @@ mod tests {
             Span::raw("hello "),
             Span::raw("world"),
         ])]);
-        assert_eq!(wrapped_row_count(&text, 4), 3);
+        assert_eq!(wrapped_row_count(&text, 4), 4);
+    }
+
+    #[test]
+    fn wrapped_row_count_exceeds_naive_ceiling_for_word_boundaries() {
+        let text = Text::from(vec![Line::from(Span::raw(
+            "one two three four five six seven eight",
+        ))]);
+        assert_eq!(wrapped_row_count(&text, 10), 5);
     }
 
     #[test]