chore: update obfs4, goptlib, snowflake (ooni#1347)

This diff upgrades obfs4, goptlib, and snowflake. I tried to import
lyrebird instead of obfs4, but that did not work as intended. It seems
tags aren't compatible with the format expected by Go (vX.Y.Z) and I did
not want to pin to the latest commit. I will report this issue to
lyrebird developers later today.

While there, also upgrade x/net and x/exp.

This work is part of ooni/probe#2524.

Here's what we could not upgrade (based on the content of `go.mod` after
we committed this diff and ran `go get -u -v -d ./...`):

```diff
diff --git a/go.mod b/go.mod
index 67e0af02..18175d73 100644
--- a/go.mod
+++ b/go.mod
@@ -80,7 +80,7 @@ require (
 	golang.org/x/exp/typeparams v0.0.0-20230522175609-2e198f4a06a1 // indirect
 	golang.org/x/time v0.3.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
-	gvisor.dev/gvisor v0.0.0-20230603040744-5c9219dedd33 // indirect
+	gvisor.dev/gvisor v0.0.0-20231006032704-15cc3fcbbd77 // indirect
 )

 require (
@@ -89,7 +89,7 @@ require (
 	github.com/alecthomas/units v0.0.0-20211218093645-b94a6e3cc137 // indirect
 	github.com/armon/go-proxyproto v0.0.0-20210323213023-7e956b284f0a // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
-	github.com/bifurcation/mint v0.0.0-20180306135233-198357931e61 // indirect
+	github.com/bifurcation/mint v0.0.0-20210616192047-fd18df995463 // indirect
 	github.com/cespare/xxhash/v2 v2.2.0 // indirect
 	github.com/cheekybits/genny v1.0.0 // indirect
 	github.com/cognusion/go-cache-lru v0.0.0-20170419142635-f73e2280ecea // indirect
@@ -132,7 +132,7 @@ require (
 	github.com/prometheus/common v0.44.0 // indirect
 	github.com/prometheus/procfs v0.12.0 // indirect
 	github.com/refraction-networking/gotapdance v1.7.4 // indirect
-	github.com/refraction-networking/utls v1.3.3 // indirect
+	github.com/refraction-networking/utls v1.5.3 // indirect
 	github.com/sergeyfrolov/bsbuffer v0.0.0-20180903213811-94e85abb8507 // indirect
 	github.com/sirupsen/logrus v1.9.3 // indirect
 	github.com/spf13/cobra v1.7.0
@@ -142,10 +142,10 @@ require (
 	github.com/templexxx/xorsimd v0.4.2 // indirect
 	github.com/tjfoc/gmsm v1.4.1 // indirect
 	github.com/wader/filtertransport v0.0.0-20200316221534-bdd9e61eee78 // indirect
-	github.com/xtaci/kcp-go/v5 v5.6.2 // indirect
+	github.com/xtaci/kcp-go/v5 v5.6.3 // indirect
 	github.com/xtaci/smux v1.5.24 // indirect
 	gitlab.com/yawning/bsaes.git v0.0.0-20190805113838-0a714cd429ec // indirect
-	golang.org/x/mod v0.12.0 // indirect
+	golang.org/x/mod v0.13.0 // indirect
 	golang.org/x/term v0.13.0 // indirect
 	golang.org/x/text v0.13.0 // indirect
 	golang.org/x/tools v0.13.0 // indirect
```

We cannot upgrade:

- gvisor because (a) we're fine with our pinned version used by netem
and (b) the main branch of gvistor is not suitable for go-getting anyway

- mint because this is the version Psiphon requires

- utls because this is the version Psiphon requires

- kcp-go because v.5.6.3 requires go1.21

- x/mod which seems to be needed by quic-go to generate mocks, so not
upgrading it isn't a big deal.

go.mod

@@ -4,8 +4,6 @@ go 1.20
 
 require (
 	filippo.io/age v1.1.1
-	git.torproject.org/pluggable-transports/goptlib.git v1.3.0
-	git.torproject.org/pluggable-transports/snowflake.git/v2 v2.5.1
 	github.com/AlecAivazis/survey/v2 v2.3.7
 	github.com/Psiphon-Labs/psiphon-tunnel-core v1.0.11-0.20230822172011-3f91b1b804b1
 	github.com/alecthomas/kingpin/v2 v2.3.2
@@ -37,10 +35,12 @@ require (
 	github.com/rubenv/sql-migrate v1.5.2
 	github.com/schollz/progressbar/v3 v3.13.1
 	github.com/upper/db/v4 v4.6.0
-	gitlab.com/yawning/obfs4.git v0.0.0-20230519154740-645026c2ada4
+	gitlab.com/yawning/obfs4.git v0.0.0-20231005123604-19f5a37fe427
 	gitlab.com/yawning/utls.git v0.0.12-1
-	golang.org/x/crypto v0.13.0
-	golang.org/x/net v0.15.0
+	gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib v1.5.0
+	gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/v2 v2.6.1
+	golang.org/x/crypto v0.14.0
+	golang.org/x/net v0.16.0
 	golang.org/x/sys v0.13.0
 )
 
@@ -74,9 +74,9 @@ require (
 	github.com/spf13/pflag v1.0.5 // indirect
 	github.com/stretchr/testify v1.8.4 // indirect
 	github.com/xhit/go-str2duration/v2 v2.1.0 // indirect
-	gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/goptlib v1.5.0 // indirect
+	gitlab.com/yawning/edwards25519-extra v0.0.0-20231005122941-2149dcafc266 // indirect
 	go.uber.org/mock v0.3.0 // indirect
-	golang.org/x/exp v0.0.0-20230905200255-921286631fa9 // indirect
+	golang.org/x/exp v0.0.0-20231005195138-3e424a577f31 // indirect
 	golang.org/x/exp/typeparams v0.0.0-20230522175609-2e198f4a06a1 // indirect
 	golang.org/x/time v0.3.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
@@ -145,9 +145,8 @@ require (
 	github.com/xtaci/kcp-go/v5 v5.6.2 // indirect
 	github.com/xtaci/smux v1.5.24 // indirect
 	gitlab.com/yawning/bsaes.git v0.0.0-20190805113838-0a714cd429ec // indirect
-	gitlab.com/yawning/edwards25519-extra.git v0.0.0-20230925102617-375edaeb7d45 // indirect
 	golang.org/x/mod v0.12.0 // indirect
-	golang.org/x/term v0.12.0 // indirect
+	golang.org/x/term v0.13.0 // indirect
 	golang.org/x/text v0.13.0 // indirect
 	golang.org/x/tools v0.13.0 // indirect
 	google.golang.org/protobuf v1.31.0 // indirect