Create new smux session for each SOCKS connection

Merged Cecylia Bocovich requested to merge cohosh/snowflake:issue/40023 into master

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).

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