fix: bump rln to 2.0.2 to match the librln actually linked

The `rln` dependency exists only to force RLN symbols into the link, but
it had drifted two majors from the library it is meant to mirror: the
vendor pins `LIBRLN_VERSION := v2.0.2` and build.rs links that
`librln_v2.0.2.a`, while this crate still asked for 0.3.4.

That drift was invisible in isolation and fatal downstream. Every rln up
to 0.6.1 pins `serde = "=1.0.163"` exactly, so any consumer resolving
waku-bindings alongside a crate needing a newer serde -- openmls'
tls_codec wants ^1.0.184 -- fails to resolve at all, since cargo will not
duplicate serde 1.x. libchat cannot depend on this crate without it.

2.0.2 relaxes the pin to ^1.0.228 and matches what is linked. Verified by
building and linking libchat against it: no duplicate-symbol clash with
the vendor's archive.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ai43sF2rymPFMG9iki9fwL

waku-bindings/Cargo.toml

@@ -30,7 +30,7 @@ smart-default = "0.6"
 url = "2.3"
 libc = "0.2"
 serde-aux = "4.3.1"
-rln = "0.3.4"
+rln = "2.0.2"
 tokio = { version = "1", features = ["full"] }
 regex = "1"
 chrono = "0.4"