mux tests memory footprint

Some of the mux tests are quite expensive to run:

* [ ] `mux send receive bidir`
* [ ] `mux send recieve`
* [ ] `miniprotocols Pipe`
* [ ] `miniprotocols Queue`

# `mux send receive bidir`

```
cabal run network-mux:test -- --quickcheck-replay=0 +RTS -t -RTS -p '/mux send receive bidir/'
mux
Mux
mux send receive bidir: OK (47.13s)
+++ OK, passed 100 tests.

All 1 tests passed (47.13s)
<>
```

# `mux send receive`
Note as bad as the former (~80MB).

```
cabal run network-mux:test -- --quickcheck-replay=0 +RTS -t -RTS -p '$3 == "mux send receive"'
mux
Mux
mux send receive: OK (24.55s)
+++ OK, passed 100 tests.

All 1 tests passed (24.55s)
<>
```

# `miniprotocols Queue`
```
cabal run network-mux:test -- --quickcheck-replay=0 +RTS -t -RTS -p '/miniprotocols Queue/'
mux
Mux
2 miniprotocols Queue: OK (10.01s)
+++ OK, passed 50 tests.

All 1 tests passed (10.01s)
<>
```

# Other tests
Other tests seem fine:
```
cabal run network-mux:test -- --quickcheck-replay=0 +RTS -t -RTS -p '!/miniprotocols Pipe/ && !/mux send receive/ && !/miniprotocols Queue/'
...
<>
```