Warm a fence's highlighting like a parse, and page the restore by rows

Two things the measurements for the previous commit turned up.

Highlighting a fence cost 174ms for a two-hundred-line Kotlin block, and
the lazy list charged it again every time that block scrolled back into
composition -- six times in one bench run, with the scroll's draw phase at
1.29ms per frame. So it is warmed and cached where parses already are:
`highlight` is a plain function taking no colour from the theme, `warm`
fills `ParsedReplies.highlighted` from `fences(parse)` off the drawing
thread, and `fenceContent` extracts the code here rather than through the
library's composable, so the string warmed is the string drawn.

And the anchor restore asked for a span counted in events, which goes
negative when the anchor's row is the oldest half-row and was coerced to
one -- a request per delta, six hundred round trips walking one reply back
a word at a time with the spinner up. It asks for a page of rows now.

Clean pairs, fresh sessions each side, same gestures. Fence scroll
(transcript-bench.sh): draw phase 0.74ms per frame before highlighting
existed, 0.77ms after, no lexing in the window either side. Streaming
forty linked items (stream-bench.sh): 2412ms of reparsing before, 674ms
after; mean 5.0ms to 1.4ms, worst 8.9ms to 7.9ms. Bullet glyphs, fence
colours, the image links and the reference link checked on the emulator;
lint clean on AGP 9.4.0.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/androidApp/src/main/kotlin/com/example/aiapp/ToolInput.kt

@@ -117,7 +117,9 @@ fun ToolInputView(tool: String, input: String, modifier: Modifier = Modifier) {
             // Not wrapped: a wrapped command hides where its arguments end,
             // and the long one is the one being read closely.
             Text(
-                highlighted(subject, parsed.language),
+                // Not cached: a tool's subject is one command line, which lexes in microseconds
+                // -- the cache exists for a fence with two hundred lines in it.
+                remember(subject, parsed.language) { highlight(subject, parsed.language) },
                 style = MaterialTheme.typography.bodySmall,
                 fontFamily = FontFamily.Monospace,
                 softWrap = false,