perf(RichTextViewer): share isMarkdown decision via CachedRichTextParser

The markdown check is purely a function of `content`, but it was a
top-level function in RichTextViewer.kt — every distinct instance of
the same content (e.g. a quoted note rendered inside its quoter,
or the same viral note shown multiple places in a feed) re-scanned
the string.

Move the decision into `CachedRichTextParser` with its own small
LRU keyed on content.hashCode(). Composables still wrap the call in
`remember(content)` so recompositions skip even the LRU lookup.

amethyst/src/main/java/com/vitorpamplona/amethyst/service/CachedRichTextParser.kt

@@ -28,6 +28,7 @@ import com.vitorpamplona.amethyst.commons.richtext.UrlParser
 
 object CachedRichTextParser {
     private val richTextCache = LruCache<Int, RichTextViewerState>(50)
+    private val isMarkdownCache = LruCache<Int, Boolean>(200)
 
     private fun hashCodeCache(
         content: String,
@@ -69,6 +70,25 @@ object CachedRichTextParser {
             newUrls
         }
     }
+
+    // Shared across every RichTextViewer instance so that the same content quoted in multiple
+    // notes only pays for the scan once. The decision is purely a function of `content`.
+    fun isMarkdown(content: String): Boolean {
+        val key = content.hashCode()
+        isMarkdownCache[key]?.let { return it }
+        val result = computeIsMarkdown(content)
+        isMarkdownCache.put(key, result)
+        return result
+    }
+
+    private fun computeIsMarkdown(content: String): Boolean =
+        content.startsWith("> ") ||
+            content.startsWith("# ") ||
+            content.contains("##") ||
+            content.contains("__") ||
+            content.contains("**") ||
+            content.contains("```") ||
+            content.contains("](")
 }
 
 object CachedUrlParser {

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/components/RichTextViewer.kt

@@ -122,15 +122,6 @@ import com.vitorpamplona.quartz.nipB7Blossom.BlossomUri
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
 
-fun isMarkdown(content: String): Boolean =
-    content.startsWith("> ") ||
-        content.startsWith("# ") ||
-        content.contains("##") ||
-        content.contains("__") ||
-        content.contains("**") ||
-        content.contains("```") ||
-        content.contains("](")
-
 @Composable
 fun RichTextViewer(
     content: String,
@@ -145,7 +136,7 @@ fun RichTextViewer(
     nav: INav,
 ) {
     Column(modifier = modifier) {
-        if (remember(content) { isMarkdown(content) }) {
+        if (remember(content) { CachedRichTextParser.isMarkdown(content) }) {
             RenderContentAsMarkdown(content, tags, canPreview, quotesLeft, backgroundColor, callbackUri, accountViewModel, nav)
         } else {
             RenderRegular(content, tags, canPreview, quotesLeft, backgroundColor, callbackUri, authorPubKey, accountViewModel, nav)