address review feedback: improve ms.zig and docs

- Simplify parse loop using for-else pattern (taylordotfish)
- Simplify jsMathRound comparison (taylordotfish)
- Fix docs: use H3 headings instead of bold text (markovejnovic)
- Clarify bundler optimization description in docs

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

docs/runtime/utils.mdx

@@ -450,9 +450,9 @@ namespace Bun {
 
 ## `Bun.ms`
 
-Built-in alternative to the [`ms`](https://npmjs.com/package/ms) package. Convert between human-readable time strings and milliseconds. Automatically optimized at compile-time when bundling.
+Built-in alternative to the [`ms`](https://npmjs.com/package/ms) package. Convert between human-readable time strings and milliseconds. When bundling, calls with constant arguments are evaluated at compile-time and replaced with the result.
 
-**Convert to Milliseconds**
+### Convert to Milliseconds
 
 ```ts
 Bun.ms("2 days"); // 172800000
@@ -469,7 +469,7 @@ Bun.ms("-1h"); // -3600000
 Bun.ms("-200"); // -200
 ```
 
-**Convert from Milliseconds**
+### Convert from Milliseconds
 
 ```ts
 Bun.ms(60000); // "1m"
@@ -483,7 +483,7 @@ Bun.ms(-3 * 60000, { long: true }); // "-3 minutes"
 Bun.ms(Bun.ms("10 hours"), { long: true }); // "10 hours"
 ```
 
-**Bundler Support**
+### Bundler Support
 
 ```sh
 $ cat ./example.ts

src/bun.js/api/bun/ms.zig

@@ -2,17 +2,11 @@
 pub fn parse(input: []const u8) ?f64 {
     if (input.len == 0 or input.len > 100) return null;
 
-    var i: usize = 0;
-
-    next: switch (input[i]) {
-        '-', '.', '0'...'9' => {
-            i += 1;
-            if (i < input.len) continue :next input[i];
-            break :next;
-        },
-        ' ', 'a'...'z', 'A'...'Z' => break :next,
+    const i: usize = for (input, 0..) |c, j| switch (c) {
+        '-', '.', '0'...'9' => {},
+        ' ', 'a'...'z', 'A'...'Z' => break j,
         else => return null,
-    }
+    } else input.len;
 
     const value = std.fmt.parseFloat(f64, input[0..i]) catch return null;
 
@@ -88,7 +82,7 @@ const MultiplierMap = bun.ComptimeStringMap(f64, .{
 // JavaScript's Math.round uses "round half toward +∞": ties round toward positive infinity (2.5→3, -2.5→-2)
 fn jsMathRound(x: f64) i64 {
     const i: f64 = @ceil(x);
-    if ((i - 0.5) > x) return @intFromFloat(i - 1.0);
+    if ((i - x) > 0.5) return @intFromFloat(i - 1.0);
     return @intFromFloat(i);
 }