fix: prevent italic regex from spanning newlines in Telegram formatter

The italic regex \*([^*]+)\* used [^*] which matches newlines, causing
bullet lists with * markers to be incorrectly converted to italic text.
Changed to [^*\n]+ to prevent cross-line matching.

Adds 43 tests for _escape_mdv2 and format_message covering code blocks,
bold/italic, headers, links, mixed formatting, and the regression case.

gateway/platforms/telegram.py

@@ -372,8 +372,10 @@ class TelegramAdapter(BasePlatformAdapter):
         )
 
         # 6) Convert italic: *text* (single asterisk) → _text_ (MarkdownV2 italic)
+        #    [^*\n]+ prevents matching across newlines (which would corrupt
+        #    bullet lists using * markers and multi-line content).
         text = re.sub(
-            r'\*([^*]+)\*',
+            r'\*([^*\n]+)\*',
             lambda m: _ph(f'_{_escape_mdv2(m.group(1))}_'),
             text,
         )