Create new smux session for each SOCKS connection
Each SOCKS connection has its own set of snowflakes and broker poll loop. Since the session manager was tied to a single set of snowflakes, this resulted in a bug where RedialPacketConn would sometimes try to pull snowflakes from a previously melted pool. The fix is to maintain separate smux sessions for each SOCKS connection, tied to its own snowflake pool.
Closes #40023 (closed).