docs(android): Note that the dropped-event session API writes to disk

Persisting the session is synchronous so the unhandled marker is durable
by the time the call returns, which means callers must stay off the main
thread. Say so where hybrid SDK authors will read it.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: buenaflor

sentry-android-core/src/main/java/io/sentry/android/core/InternalSentrySdk.java

@@ -276,6 +276,10 @@ public static SentryId captureEnvelopeNonTerminating(final @NotNull byte[] envel
    *
    * <p>Do not call this for events dropped by {@code beforeSend} or ignored exception types.
    *
+   * <p>Persisting the session is a blocking disk write on the calling thread, so call this off the
+   * main thread as the hybrid SDKs do. It is synchronous on purpose: a deferred write would not be
+   * on disk yet if the process dies right after this returns.
+   *
    * @param crashed {@code true} if the dropped error was unhandled ({@code
    *     mechanism.handled=false})
    */