Always double reconnection delay and add jitter (#35337)

Previously, we would pick an exponent between 0.5 and 2.5, which would
cause a lot of clients to try reconnecting in rapid succession,
overwhelming the server as a result.

This pull request always doubles the previous delay and introduces a
jitter that can, at most, double it.

As part of this, we're also increasing the maximum reconnection delay
from 10s to 30s: this gives us more space to spread out the reconnection
requests.

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <git@maxdeviant.com>

crates/collab/src/tests/integration_tests.rs

@@ -842,7 +842,7 @@ async fn test_client_disconnecting_from_room(
 
     // Allow user A to reconnect to the server.
     server.allow_connections();
-    executor.advance_clock(RECEIVE_TIMEOUT);
+    executor.advance_clock(RECONNECT_TIMEOUT);
 
     // Call user B again from client A.
     active_call_a
@@ -1358,7 +1358,7 @@ async fn test_calls_on_multiple_connections(
 
     // User A reconnects automatically, then calls user B again.
     server.allow_connections();
-    executor.advance_clock(RECEIVE_TIMEOUT);
+    executor.advance_clock(RECONNECT_TIMEOUT);
     active_call_a
         .update(cx_a, |call, cx| {
             call.invite(client_b1.user_id().unwrap(), None, cx)